Fesnel Lens Screens - Any Drawbacks?


White Lighter

I have been seriously considering a Tosh rp, either 42WH36 or the 51" version. I know that the crt focus is not usually set very sharply and can be improved, and that in Currys they seem to look a lot worse than they should do.

I have read the very informative info on setting up the Tosh rps by Demon and Nathan- excellent.

I wonder if compared with conventional CRT displays and even plasma, the fresnel screen has a softening affect on the picture, thereby necesitating (bad spelling) a longer viewing distance.

This would be strange as a fresnel lens has the effect of condensing and directing the incident light from the CRTs into a parallel light output, for a better view. -So who knows???

I only mention this, because I know the Tosh rps can have a fantastic picture, but in Currys, the only place I have to view them, the picture resembles murky VHS- hardly inspiring!!!

To see any scan lines at all (in natural mode) I had to stand with my head a couple of inches from the screen- hense poor focus?

I emailed Tosh about the viewing distances from a 42WH36 and a 51WH36 and they replyed the next day- very good- that they reccomend 3 to 8 m !!!!! Thats 9' 10" to 26' 3" in old money.

If I buy a large TV, I don't want to have to sit in the next room to view it- it would look Tiny!!! Incidentally, my eye to screen distance will be exactly 9 feet.

Anyway, just for comparison, Sony reccomend a minimum distance of 1.7m (5' 7") for their 44DX2 (42.5" actual size), which I suspect to be a little on the close side, but better than 3-8m!!

So Demon if your reading this, is it possible to improve the focus dramatically from murky VHS type pictures, to ones I can comfortably watch from 9 feet away, without thinking they are soft?

Thanks all, Pete.:eek:

Well at 9 feet it should be fine, thats about the distance i sit from mine (51WH36P), maybe a little less. I havent done the focus on it still (had it a fair few months now) as it does need to doing mostly on the blue, fringes a little, but at that distance it is perfectly fine. I had a plasma (panny 42PWD6) before this, returned it due to problems with plasmas that I just couldnt stand when paying 3k+ on a screen (banding, dithering, brightness fluctuations) the plasma had better sharpness than the RP but on the plasma at that distance I could see the dithering that the plasma would produce, people say dont sit with your head next to the screen when watching it then if you dont want to see the dithering, I dont, sorry but i just must have good eye sight. (just saying I was very picky about the screen i got including the Tosh)
Anyway back to the RP, I found that it was fine with the factory settings, just a little convergence and brightness and contrast settings needed changing for a half decent picture at 8-9feet so if you are going to be doing the electronic and mechanical focus (which i would like to do but am a little scared to :) ) it should be great.
No complaints with my 51 either.. considering the size, the picture can be amazingly sharp..

I always think RPTV's look awfully soft in the shops, but I am sure all RPTV owners will tell you that their RPTV looks as sharp as any CRT from normal viewing distances (8-9 feet)..

I am amazed how well even crappy sources such as VHS look on my 51".

I could never guarantee that you would not find the picture slightly soft, since the laws of physics apply, the source only has a limited number of lines, and therefore information, the larger this becomes, and the closer you look, the more you think it looks soft.
For example, take a picture of some grass on a 2megapixel camera, then print it out on a piece of A4, and a piece of 6*4, the A4 photo if you look close (10-20cm) will appear softer, the 6*4 will be sharp, and you will be able to see every blade of grass, now move these 2-3 feet away, and the A4 now looks nicely in focus and you can see all the detail of the grass still, yet the 6*4 starts to lose detail, since its so small, your eyes cannot make out the individual blades of grass anymore..

a 51" TV has almost exactly double the area of a 36" set... so what this means is
Sitting 9 feet away from a 51" TV is like sitting 4.5 feet away from a 36" TV..

And in the shop, remember that when you compare a 36 and a 51" at the same distance, the 51" picture is actually effectively magnified by 2..

I am quite fussy myself, and despite having contact lenses, my vision is excellent, and I have a thing about sharpness, yet I find the RPTV more then acceptable.. My biggest gripe with smaller CRT's is what I call detail compression, due to all that detail being on a small screen, and you being so far away at normal viewing distances (8-9 feet), you can't actually distinguish all the fine detail anymore, since your eyes do not have sufficient resolution. The 51" lets me see all the detail wherever I am sat... I could of course buy a 36" and just sit a damn site closer, but then you start to notice all the geometry flaws etc...

just some food for thought...
At the moment I'm ruling out CRT rear-projectors because the box underneath means I have nowhere to put four AV separates and a center speaker. The layout of my living room means these must go above or below my TV screen.

I've tried to visualise having a shelf on the wall above a Toshiba, but I can't see it looking very good, with 10-15 cables/wires having to go up to the shelf.

How do you Tosh owners solve this? Even if you don't have my constraints, where do you put your center speaker?

One last question - presumably I would be be mad to consider a 51" set given that my view distance is seven and a half feet?
Your set-up looks really nice - thanks for the photos, I hadn't considered the Sony - I will now. I should have thought of it before, as I knew their LCD sets let you use the built in speakers as a centre.
The Tosh's come with optional cabinet that allows some AV Equipment/centre speaker to be put under the set, and I believe some people have been putting their centre speakers ontop of the set as well, I have a largish B+W centre speaker, that fits very nicely on top of my 51...

Toshiba brochure

I wouldn't advise using the sets built in centre speakers in 5.1 surround system, simply due to poor quality and lack of tonal matching.. but saying that this is possible with nearly all RPTV's...
Thanks bond007 and Demon.

I usually find that going by the height of the screen rather than the area is more useful for comparisons, but I can see what you mean!

It's interesting that with the 42" the line size is around 0.91mm but with the 51" it only rises to around 1.1mm. I don't think it is possible to see a fith of a mm (based on 576 line display), therefore the picture you see on a 42 incher has to all intents and purpose, the same resolution definition as a 51 incher!!! Bizzzzarrr huh?

The problem I have at the moment is can paying around a third more be justified in my mind for the extra size of the 51" version?
That said, what's the point of buying a large screen rp if you just go for a run of the mill 42"?

Anyway, back to my original question of does a fresnel screen impose any softness to the PQ?
Cheers everyone, Pete.:eek:
Originally posted by White Lighter
Anyway, back to my original question of does a fresnel screen impose any softness to the PQ?
Given that RPTVs are used widely for high definition tv in the USA, that would have to be a no. If focus is set correctly, RPTVs can resolve at the maximum capability of dvd - 6.75Mhz. Fixed pixel displays, such as plasma, often look sharper, but that's because you're seeing pixel edges. RPTVs don't suffer from the artifacting associated with fixed pixel displays; a well set up RPTV looks extremely detailed, but smooth. The fresnel screen does impose viewing angle and distance limits, however. Vertical viewing angles are generally tight, but there isn't as much a problem in the horizontal plane. RPTVs will look terrible if you look at them standing up from a couple of feet away.
Originally posted by Demon
I wouldn't advise using the sets built in centre speakers in 5.1 surround system, simply due to poor quality and lack of tonal matching.. but saying that this is possible with nearly all RPTV's... [/B]
You're right about tonal matching, but that's an issue with matching any centre speaker. The PS2 RPTV is designed to be used as a centre speaker - there are speaker terminals on the back of the set. The quality is much higher than you would think, but this tv cost the best part of £3k when it came out, so high quality components are used throughout. My front speakers are the highly regarded Dynaudio Audience 50's, my sub is an REL strata and the RPTV's centre is not embarrassed in this company and actually improves on my old Mission centre. It's a question of convenience for me, but a matched, dedicated centre is likely to be the better option for most people.

When you say it is possible with nearly all RPTVs to use them as a centre speaker, can you explain how? Do you mean feeding a line level signal into the tv's amplifier? That would indeed be crap.
The PS2 RPTV is designed to be used as a centre speaker - there are speaker terminals on the back of the set

Nuff said.. if you are satisfied with the TV's speakers as a centre, considering your setup, I'd not complain..

When you say it is possible with nearly all RPTVs to use them as a centre speaker, can you explain how? Do you mean feeding a line level signal into the tv's amplifier? That would indeed be crap
For my Brother's previous RPTV, we simply replaced the sets internal speakers with some much higher quality items, and since it already had a set of spring clip connections on the back (These where for external front speakers), we simply 're-used' these and wired them directly to the internal speakers..

Not quite as easy, or straightforward as the Sony, and potentially warranty invalidating, but it did do the job.. and we used the same drivers as found in his front speakers, so Tonal matching was quite good..

Bobones has a good point about the Fresnal lens, it does allow the full 6.75Mhz of information to be displayed, so is as sharp as the source material is capable of.. and having seen many RPTV's I wouldn't give it a second thought..
Originally posted by cjking
Your set-up looks really nice - thanks for the photos, I hadn't considered the Sony - I will now. I should have thought of it before, as I knew their LCD sets let you use the built in speakers as a centre.
Thanks for the compliment, I'm really happy with the set. It's actually an older Sony model which has features missing from the current Sonys (including the centre speaker thing, DRC-MF, twin-tuners). Robert Whyte's are still selling these graded sets for £799 + del, which is a bargain considering they cost £2.8k when they came out. Mine is a graded set but it was to all intents, brand new, flawless and has a standard Sony 12month warranty

The current Sony is the KP44DX2 with a RRP of £1800. The current (April) Home Cinema Choice has a review and they love it. As they say, "It's one of the best rear projection TV's we've ever seen. And, perhaps even more importantly for its chances of success, it gives its only real rival at the moment, Toshiba's 42WH36, an unexpectedly sound thrashing".
Strangely, I've just been in Curry's (Next to Tesco's.. we where doing the weekly shop) and they've got a 44DX2 next to a 42wh36..

I can only summise that they didn't review these 2 particular RPTV's, the wh36 had an amazing amount more detail and clarity, despite being poorly converged... The DX2 looked soft in comparison, and the detail , even on a poor source seemed lacking, it was just too smooth. Although I am sure you get good and bad examples of all models, the Sony 44DX2 I saw had no visible line structure, and the black bars above/below the broadcast content where a little soft, perhaps this is just a bad example? or perhaps reviews only place a small amount of emphasis on PQ, the rest being features etc..?

Interestingly they've also got the Samsung 46" LCD, and the LG 44 DLP, all side by side with the wh36 and the DX2, and doing a quick comparison of focus/detail etc, the Tosh does seem to stand out as being quite good, the samsung loks soft with terrible blacks, the LG has artefacts and looks grainy, and this particular DX2 looks soft, with a badly reflective screen..
The review actually marked the DX2 down on features, connectivity, and analogue tuner picture, but praised it for pq, sound and looks. It gets 4 stars for features, 5 for picture and sound, and a Best Buy guarantee award.

I don't think you can really assess the quality of these sets looking at them in Curry's. You need to be sitting down at the right distance, and use something like Avia and a few well transferred dvds to really assess their qualities. What may look impressive in the shop - a brighter, more vibrant, sharper image - may actually be due to too high contrast, over-emphasised reds and excessive edge enhancement.

My Sony is a different beast from the DX2, but I am extremely impressed by the natural, detailed images it produces. Avia backs this up this subjective view with fantastic results in terms of geometry, convergence, resolution and colour decoder accuracy and linearity. It's hard to see where the picture quality can be improved.

Since disabling svm (a type of edge enhancement) , images on my set do seem smoother, but they are in actual fact more accurate and detailed. Smoothness shouldn't be confused with softness, and sharpness doesn't necessary equate with detail. See this page for a nice demonstration of this.

I have no doubt that the Toshiba sets are great value for money, have superior connectivity options, and offer great images, but the Sony's deserve a bit more respect on these forums imo.
oops wrong thread!

I agree, although I am not sure people are dissing Sony RPTV's, I must admit, that of all manufacturers, the most grown up sets in terms of features/build quality seem to be Sony.. I am a bit of a sony man at heart, I have had loads of Sony home cinema stuff...

Don't panic, I wasn't confusing smoothness with softness either.. just looking at grass/tree bark in the LOTR trailer being played, it was clear how much detail was lacking on that particular DX2...

Like you say, its hard to review sets in curry's, but one thing I can say with hand on heart, all RPTV's seem of variable quality, you get good and bad examples of all manufacturers, and this highlights two things (the problems may well be due to mechanical stress caused by transport.. remember these things are large, and to some extent a bit flimsy..)
1. You should be prepared to tweak.. this is not necessarily a bad thing, you can return a set for poor geometry, but who's to say the next one will be any better, best to DIY IMHO..
2. Remember this must occur with a lot of the reviews.. if they get a badly setup example, they will quite rightly slate it....

And as for Sony RPTV's getting more respect in these forums, I agree, in fact, all RPTV's need to get more respect in these forums, it seems strange how over 90% of RPTV owners would loathe going bcak to a smaller direct-view CRT.. must say something.. and at last RPTV's look nice, especially the sony/samsung cabinets..
Yup well said Demon. THere would be no way that I would ever go back to direct view. It a shame that Sony & Tosh dont make sure that the sets are converged on site it there big outlets. I have recently been considering WH36 but my local store that stocks needs a service menu converge. I done the user one but as you are aware it only does the edges. Sales manager querried what I was doing and was impressed with the results but now the middle looks terrible in comparison. Shame I didnt have your instructions for the proper converge. I asked him if he could get Tosh in to do it and he just sort or smirked. It would surly be in Tosh's interest and the store to get it done. Hell I might even do it for them if they will give me a discount on the set.
yeah.. absolutely.. I can't imagine the amount of sales that are lost because of poor setup.. :rolleyes:

If I was the store manager, I'd have DVD players hooked up to each one, and have them setup using AVIA or something, and properly converged! although I can only imagine that they don't need to, since Average Joe just probably bases his whole decision on the cabinet colour, or design, and as long as there is a candle flickering in the back for a picture, that'll do... ;)
Store that I was viewing in had 3 Tosh's, Thompson, Samsung and one other and all of them were like old 80's pub ones. I cannot see that they would sell a single set with how badly converged they are. They actually have the cheek to have them switched on as well. Some of the the convergence is showing 10mm fringes around objects. What gets me is you have sales staff who are sat around doing nothing and surely one off them has some interest in AV and could spend hours a day perfecting the sets and he/she should then be in charge of the sales of that type of set and get some commision on the incresed sales that they would get.
Thanks bobones for your reply on Fresnel screens in America.

I can't imagine the amount of sales that are lost because of poor setup.

Was shopping in Halifax on Sat. and happened to pass by one of those overpriced 'rent-a-tv' type shops. What caught my eye was in the window- a fully set up Tosh 42WH36 rp with a digital feed to it. They had it on a stand - sensible to bring the punters in and although the contrast was obviously set too high (being in directish sunlight), the picture just blew me away.

This is the first example of a properly set up rp I have seen and what a treat. I will be saving some more pennies to get the 51.:D

By the way, been thinking more about what you were saying about viewing distances (eye to screen) for rp and have come up with the following:

For any given ratio of rectangle, in this case a 16:9 screen, doubling the height will produce a corresponding 4X increase in area. (standard basic maths). Now from this, you can see that the actual area of the screen is not the critical element in deciding how far back you sit from the screen.

So for a 36" CRT (visible screen size 33.9") the height of the screen is 16.6 inches. Now as it has been braudly established on this forum that for a 50/51" rp the seating distance should be approx 9 feet and the height of the Tosh 51" (actual screen size) is 25.1 inches therefore this makes the 51" approx 1.5x the height of the 36"

Still with me, (I sound like Jonny Ball on Think Of A Number. Anyone remember that?). Right, now if we devide 9 feet by 1.5 we get 6 feet. Therefore a doubling of screen height say from a 36" to a 51" gives a viewing distance of half as much again i.e. 6ft to 9ft which is not the same as a halving of distance as you hinted at.

So for a 36" CRT viewing distance is 6Feet
42" Tosh rp =7 Feet 5 inches
51" Tosh rp =9 Feet.


If you don't believe me, try this:

Take a 2" high plastic plant pot and a 4" one.
Find a long kitchen table or bench etc.
Measure the table and place the 2" pot in the centre.
Go to the other end of the table and place the 4" high pot there, directly in line with the 2" one.
Now view from the end of the table (bend down) without the pot.
Heh-presto the smaller pot now obscures the larger one at half the distance for half the height!!

......I really must get out more...

If anyones interested, why buy expensive black cloth to line the insides of an rp when you could just paint it with inexpensive matte black blackboard paint!

Thanks for your input everyone. It's cold up north!

Regards, Pete:eek:
I have a 44" which I normally watch from about 10ft. I only need to move my chair forward by 1.5ft for the same effect as a 51" screen. If I move my chair to the minimum recommended distance for my screen (5.5ft) it's just like watching an 7ft screen from my old seat! Why pay more? :smoke:
which is not the same as a halving of distance as you hinted at

Damn, thats a head do-er

You are correct... of course.. nice plant pot analogy... I was making some rash assumptions there... :blush:

But.. and its a big BUT..
just looking at the area's..

36" TV, aspect ratio 16:9, gives W*H of 31.38" * 17.64" = ~553 Sq Inches..

42" TV , same aspect gives W*H of 36.6" * 20.5 = ~750 Sq Inches...

51" TV, same aspect, gives W*H of 44.45 * 25 = ~1111 Sq Inches..

so for any given distance, the 51" TV has twice the viewable 'area' as a 36" TV.. and 1.5 times that of a 42"....

Which does make a big difference....

How big the image looks from a given distance is determined by how much it occupies your field of vision. In other words the angle between your head and the edges of the screen is what's important.

In order for a 42" set to fill your field of vision to the same extent as a 51" set from 9ft, you need to move closer so that this viewing angle is the same. Keeping the angle the same is equivalent to keeping constant the ratio of the distance from the screen to the screen size.

So for a 51" screen at 9ft (108"), the ratio is 108/51, so a 42" screen needs to be 42*108/51 = 89" (7'5") away to appear as big. A 36" screen needs to be 36*108/51 = 6'4" away to appear as big.

When you consider that a 50" plasma screen costs £2k more than a 42" screen, moving your sofa 1.5ft closer might be the better option :D
But.. and its a big BUT..

Demon, thanks for the reply.

Yes you're right about the area it's amazing how we can watch so massive images at this resolution!

By the way, remember most TVs quote the CRT size including overscan, so the actual viewable screen of a 36" is actually 33.9".
That of a 32" is 29.9", which is why some of the LCD flat displays are 30" with no apparent overscan!

To confuse matters even more for punters, the Tosh rptvs are actually 42,51,57 ..etc with the overscan on top tof this. Measure it yourself! This means that if you wanted to, demon, you could tell people that you have a 53" TV.

Then again boasting about size doesn't really do anything for me (not that you do). These TVs are just BIG, and that's enough for me.

About the area of screen issue- I think I've been thinking about it too much. Sometimes it's better to just get on with life and watch a damn good film on a TV that does it justice. I am a Technician, though, so things like this just peek my interest!

I'm waiting with trepidation to see what slagging offs our humble 576 line TVs are going to receive in the wake of the emerging Hi-Def revolution. Me, I'm quite happy with what we have at the moment and don't intend to rush out and buy a load of expensive new 'Super-Duper' Hi-def kit, to watch the same old repeats, etc.

It anoys me sometimes when certain reviewers in a certain AV magazine, who and which will go nameless, (Mr A you know who you are!), say that the new plasma or other has ok PQ with normal sources. When fed with HI-def from their labs, low and behold it produces a fab PQ and gets a Best Buy.:mad:

Anyway people pay their money and make their choices. There is too much anger in the world as it is, so I won't add to it. ....Hoorahh for diversity.

I better go now cos I seem to be rambling- what did you think about the black paint idea?

Best regards everyone. Peace from Pete.:eek:
The black paint idea sounds good, much cheaper, and easier to apply.. and I suppose any 'gaps' could be filled with cheap matt card, even sprayed with the matt paint..

We have a family member coming over from the states that is thinking of bringing his 53" Hitachi Widescreen HDTV over with him, since its 'worthless' over there... be nice to see a HiDef Tv in the flesh!!!

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