scopeless lens build lens .. help reqd..

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russman4
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Joined: 16 Sep 2014, 07:45
Location: chertsey surrey

scopeless lens build lens .. help reqd..

Post by russman4 » 22 Jul 2015, 09:33

chaps .

built my first scopeless rig , with a sb tube , 50mm lens , ian sirrel torch and home build screen housing .

really chuffed with the result , but found it to be lacking in the mag department, so went about improving ,

I then bought a 135mm slr lens , a cheapie £20 pentax off flea bay .

on fitting this lens , I now have 2 problems

First was I found I had to move the camera further down the tube to get it focused , (had to tap new 3mm allen key threads)
second was I couldn't get the damn thing to zero , it was appearing the camera is moving (?) or the lens has movement . Not sure whats up . Any one got experience of the 135mm lens on the scopeless rig ?

Any ideas of a fix , or suggestions for a good 100mm or 135mm lens

thanks
russ m

phoenix
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Re: scopeless lens build lens .. help reqd..

Post by phoenix » 22 Jul 2015, 10:04

A cheapo 135mm lens is definitely NOT going to work in a scopeless build
Zoom lenses won't work in a scopeless build because adjusting the zoom affects the POI.
Your best bet is a fixed focal length Cosmicar 75mm f1.4, but they are not easy to find and have become quite expensive.

Cheers

Bruce
LAND ROVER - THE WORLD'S WORST 4X4 BY FAR

Jirka
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Re: scopeless lens build lens .. help reqd..

Post by Jirka » 22 Jul 2015, 10:58

Zoom lenses can be used in scopeless builds if you just use the zoom capability to find the focal length that suits you best and then lock the zoom ring. Or if you design a reticle that will show multiple POIs for various zoom settings.

The bigger problem with cheapo zoom would be the speed I think.

I agree the Cosmicar is one of the best lenses you can get. I would add a few more affordable lenses to the list:

- Computar 12,5-75/1.2
- Cosmicar 12-5-75/1.8 (slower, but still good)
- Nikkor 85/1.8 (older versions are pretty reasonably priced)
- Nikkor 50/1.4 (again, older versions)
- Canon FD 50/1.4

Good fast zooms like the Cosmicar became more expensive recently because they are popular among the users of mirrorless cameras.

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some bloke
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Re: scopeless lens build lens .. help reqd..

Post by some bloke » 22 Jul 2015, 11:45

Hi, had no problems with my 135mm lens. You may find it easier to crop some of the threaded area of the EJ230 tube off so you can move the camera forwards again. Closer moves infinity more to the midrange area of adjustment - we don't need the macro end for our purposes.
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terry1001
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Location: Ipswich, Suffolk

Re: scopeless lens build lens .. help reqd..

Post by terry1001 » 22 Jul 2015, 20:59

I'm guessing that as you're using one of Daves mounting tubes you're probably using M42 threaded lenses. You can get 135mm f2.8 lenses which aren't too bad if a bit slow and I find that the magnification is a bit too much for me although you may find it ok. My preference is for something around 85mm to 105mm but it might take a while to find a decent one.
As has been said zoom lenses are a bit of a non starter because they are generally very slow and the zoom has to be locked which is a bit of a bodge so a fixed focal length one is a better bet. Decent lenses do come up on ebay fairly often but they are going to be more expensive because a lot of people still use them with various adapters.

Paul1961
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Location: Melbourne, Australia

Re: scopeless lens build lens .. help reqd..

Post by Paul1961 » 22 Jul 2015, 21:50

Could be your lens causing zeroing issues but before you rush out and spend more £'s, does the 50mm hold zero after having moved the camera forward? Could be the 135mm lens is ok but the camera may not be stable with the new position it's now in.
What are the specs on the 135mm lens? Some Pentax lenses aren't too bad.

russman4
Posts: 28
Joined: 16 Sep 2014, 07:45
Location: chertsey surrey

Re: scopeless lens build lens .. help reqd..

Post by russman4 » 23 Jul 2015, 17:30

thanks for all the replies boys , appreciated

the 135mm lens was a m42, I added a cs mount to m42 convertor , the optics with the camera were ok , I just had to move the ej230 further down inside the tube to get it focused, and tap 3 new allen keys further back to hold it in its new position .

just cant understand why I cant zero it , every time I tried a correction it would be out the next round , !

cheers


russ man

terry1001
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Re: scopeless lens build lens .. help reqd..

Post by terry1001 » 23 Jul 2015, 18:48

I should have mentioned that focussing the lens can cause movement of the optical axis of the lens which can alter your point of impact, it doesn't always happen but with longer focal length lenses you do have to alter the focus more often as the depth of field is much less. The method I used, and this was on an air rifle fitting, was to focus the lens using ir in the dark at a distance which gave reasonable results across my shooting distances and lock it in that position. In daylight I improved the depth of field by setting the lens to f16 which also helps cut the light reaching the sensor so that the gain doesn't have to work over such a wide range. If you want to set the gain manually to get maximum performance in the dark you will have to really cut down the amount of light in daytime.
Depending on which 135mm lens you have it may be quite a bit heavier than the 50mm and the weight could be causing movement of some of the parts. You should also check for any slack in the threads between lens and camera just in case.

Mr. FOG
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Re: scopeless lens build lens .. help reqd..

Post by Mr. FOG » 24 Jul 2015, 03:57

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thank

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