Pin Cushion help please

**canary_jules** · **05-03-09, 06:08 AM**

Hi, I recently purchased a 2nd hand HTB-AR lens. However, the prisms moved when in transit (damage claim is currently active with UPS). In the meantime I have tried to replace the prisms although I'm not sure I've been totally accurate. Using the lens my images are trapezoid shaped with the image being wider at the top (particularly the top right) than the bottom. If I tilt the lens so as to correct it then areas of the image (particularly toward the top left corner) go out of focus. It's really frustrating. Can anyone offer advice?

**Prof.** · **05-03-09, 07:37 PM**

Hi canary jules and welcome..

If your prism's are aligned correctly and the image is widened to the edges of the side borders, then tilting the lens slightly should offset any trapezoid effect..

I would suggest that you place the lens in front of the projector with the lens case open, and adjust your front and back prism's, to just display a little over the side borders..
Don;t be concerned if the image looks a bit trapezoidal, and when you're happy with the width of the image, close up the lens case and then tilt the lens to offset any trapezoid shape..
Is your projector floor mounted or ceiling mounted.?

**canary_jules** · **05-04-09, 03:10 AM**

Hi, thanks for the reply. It's ceiling mounted - which obviously makes such adjustments tricky. The thing is there are areas that go out of focus if I adjust the lens by tilting it. I have to position the lens in a very precise position because of this - so as to avoid the image passing through the top of the prisms. Actually, if I take the lens down and simply look through the prisms I can see whatever I'm looking at shift slightly. There are areas of distortion in the glass which relate to the out of focus areas on the screen. So my feeling is that I'll never be able to 'dial' this out. I bought the lens 2nd hand on another forum just recently.

**Prof.** · **05-04-09, 08:21 PM**

Quote:

canary_jules wrote:

Actually, if I take the lens down and simply look through the prisms I can see whatever I'm looking at shift slightly. There are areas of distortion in the glass which relate to the out of focus areas on the screen. So my feeling is that I'll never be able to 'dial' this out. I bought the lens 2nd hand on another forum just recently.

That is really bad..There should be no distortion in the glass of the prism when you move it around..It should be just like looking through a window..
They are obviously faulty prism's and if I were you, I'd be asking for my money back..

Failing that, you could ask HTB to sell you some new prism's..From what I've heard, they seem to be very co-operative people..

**canary_jules** · **05-05-09, 01:11 AM**

Indeed they are! Randy at HTB has been guiding me through via email all the way. He's been truly superb! Alas, however, HTB have confirmed that since it was manufactured in 2007 my lens isn't under warranty any more so I'd have to buy a new prism, which is what I'll probably have to do. BTW, if anyone is interested they told me that they have a new model lens coming out later this year with a more compact housing, so something to look forward to there!

The sort of good news is that I have been able to minimise the distortion so that it barely appears at the top of the image. However, that is at the cost of geometry - I have to tilt the lens forward significantly so that the light beam passes underneath the area of distortion. Thus the image still looks pretty trapezoid and I'm on the edge of cutting off the bottom of the image as the light beam catches the bottom of the lens. If I try and straighten the lens I introduce more distortion. I don't think I could live with the image as it is now, so it looks as if, as I said, the only route open to me is to buy a new prism. Still, if UPS deliver (now that's an ironic joke!) on the damage claim, refund me my customs bill and the carriage cost then even with a replacement prism this lens will have turned out to be a very reasonable buy indeed.

**mitch3** · **05-10-09, 10:42 PM**

seting up an anamorphic lense is not easy, and you should be able to get the picture just right if you keep messing with the prisms and adjusting them until the picture is how you want it.

**canary_jules** · **05-12-09, 09:06 AM**

Well I have my received and installed my replacement prism. Randy at HTB has been amazing. I can truly say that HTB's customer support has been fantastic - and that has been despite the fact that until I bought the replacement lens from HTB I wasn't directly one of their customers.

In any case I have the prism in situ so I now need to work on getting the lenses properly tuned. My geometry seems fine to my eye apart from the fact that I'm getting much more CA on the right than the left of the image. The CA is quite noticeable and starts from just right of centre. What do I need to do to adjust this?

Thanks for your advice guys.

**Prof.** · **05-12-09, 07:47 PM**

Quote:

canary_jules wrote:

In any case I have the prism in situ so I now need to work on getting the lenses properly tuned. My geometry seems fine to my eye apart from the fact that I'm getting much more CA on the right than the left of the image. The CA is quite noticeable and starts from just right of centre. What do I need to do to adjust this?

I had the same problem with my lens..Left side virtually no CA..right side, clearly visible CA..
On the DVE test pattern it was very obvious on the right side, but fortunately not as obvious when watching a movie..
I tried re-aligning the back prism, even tilting it slightly but could never improve on it very much..

The other day I decided to re-check the alignment of the projector to the screen and found that it had twisted slightly to the left..even though the image was still centred on the screen..
The reason it was still centred is that I'm able to twist the Anamorphic lens slightly, to the left or right..which moves the image to the left or right..if you follow all that..

So in a nutshell, both the projector and the lens were not square to the screen..

I straightened it all up and then measured the distance from the side walls to the centre of the proj. lens..Perfectly centred..

The end result is that I now have less CA on the right side and a little on the left side..The best you can ever have with a two prism lens..

It might be worth double checking your alignment..

**canary_jules** · **05-13-09, 01:20 AM**

Thanks for that advice. I half suspected that the alignment of the pj and lens to screen might have something to do with it. I'll have a go at adjusting the projector in its mount to see if it helps.

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