Telecentric combo at 0.8X to 1.69X
Moderators: rjlittlefield, ChrisR, Chris S., Pau
-
- Posts: 318
- Joined: Thu Sep 22, 2011 9:55 am
- Location: Florida
Hi Rik,rjlittlefield wrote:Well, it's a tradeoff. With the added aperture you have to change extension at the camera, where with the added lens you have to change extension between lenses. It seems the same amount of trouble either way, and with the other advantages of added-lens versus added-aperture, I see the scales tipping toward added-lens most of the time.killes wrote:This is exactly the reason why I did not want the "lens in front" approach, I thought the changing distance would be a problem.rjlittlefield wrote:However, that lens has one very nice feature: the entrance pupil maintains a constant distance from the front of the lens as focus changes. This simplifies the added-lens approach because no change in separation is required as the lens ring is turned to change magnification/focus.
sorry for not getting back to you sooner!
I've now found my setup to be not very well working. There are two issues with it:
1) the extension. The extension helps with the magnification, but also takes away light. This makes it hard to do hand-held photo in 1:1.
2) the lens. The 50mm lens I used is old and the images aren't as sharp as I am used to from my macro lens.
So I guess I'll see if I can find a used Raynox somewhere.
Cheers,
killes
- rjlittlefield
- Site Admin
- Posts: 23625
- Joined: Tue Aug 01, 2006 8:34 am
- Location: Richland, Washington State, USA
- Contact:
- rjlittlefield
- Site Admin
- Posts: 23625
- Joined: Tue Aug 01, 2006 8:34 am
- Location: Richland, Washington State, USA
- Contact:
Using a Mitutoyo M Plan Apo on such a short tube lens will give soft and aberrated corners even on APS-C. Whether the limit is 150mm or 125mm or 100mm or 90mm is largely a matter of taste. If the subject fills the frame you'll need the longer lengths; if the edges and corners are mostly for context and don't have to be sharp then the shorter lengths will do. I've published tests of the 20X on 125mm HERE, and the 10X on 100 mm HERE.pierre wrote:Sorry for the bother, but I was a bit puzzled seen the use of a 90mm for a Mity. I was guessing this big guy would not work right under 150mm.
--Rik
- rjlittlefield
- Site Admin
- Posts: 23625
- Joined: Tue Aug 01, 2006 8:34 am
- Location: Richland, Washington State, USA
- Contact:
- rjlittlefield
- Site Admin
- Posts: 23625
- Joined: Tue Aug 01, 2006 8:34 am
- Location: Richland, Washington State, USA
- Contact:
This is not yet completely telecentric. If you shift and overlay the image, as shown below, you can see that the sticks still look bigger in the foreground than they do in the background. Notice that the cyan line lies smoothly along the edge of a stick, but the orange line has to break where the images are overlayed.Guido wrote:Is this comming Close, I notice focussing that there is a difference.
This sort of test is very strong, but it works better if
1) the sticks run straight up and down in the photo (instead of diagonal), and
2) you stop down a lot when the picture is taken so that the background is pretty sharp too.
This sort of test can also tell you how to adjust the position of the achromat. If the foreground is bigger than the background (normal perspective), then move the achromat farther in front of the normal lens. If the foreground is smaller than the background (inverted perspective), then move the achromat closer to the normal lens. When the achromat is at the perfect place, foreground and background will be exactly the same size.
Your test indicates that the achromat needs to be moved farther in front.
--Rik
Telecentric Lens
Can one make most lenses near telecentric by using combos such as a Raynox 250 or other combos? How does one test a lens setup for telecentricity?
Robbie
Robbie
Re: Telecentric Lens
Robbie,RobbieC wrote:Can one make most lenses near telecentric by using combos such as a Raynox 250 or other combos? How does one test a lens setup for telecentricity?
Robbie
If you do a search here you'll find a number of threads on the subject. I believe Rik found that putting a Raynox 250 in front of a Canon 100mm macro produced a telecentric result, I tried with a Nikon 105mm macro and got a somewhat telecentric result.
A simple test is to look into the lens front with something with infinity focus, and look for the iris (stopped down so you can see it better) to be in focus. As Rik did, I used my long glasses and eyeballed it. But wasn't sure so I used another technique described here to use a long lens focused at infinity on another camera and look at the iris. I used a 300mm, and my eyeball was close.
Hope this helps,
Best,
Mike
Re: Telecentric combo at 0.8X to 1.69X
Here, I've got loaned too a little Raynox 250 from local photographer Torbjørn and tested it as telecentric add-on; with a vintage 55mm and a newer 90mm macro.
It works well indeed; only issue is that it is a bit small, so it is useful only for large magnification.
Precise telecentricity can be obtained with most objectives, just put it at the right distance from the host macro.
Its little brother (150) or its larger brothers (DCR 5320) may be useful for telecentric with longer macro objectives (150, 200mm).
https://patta107285337.wordpress.com/20 ... d-on-lens/
.
It works well indeed; only issue is that it is a bit small, so it is useful only for large magnification.
Precise telecentricity can be obtained with most objectives, just put it at the right distance from the host macro.
Its little brother (150) or its larger brothers (DCR 5320) may be useful for telecentric with longer macro objectives (150, 200mm).
https://patta107285337.wordpress.com/20 ... d-on-lens/
.
Re: Telecentric combo at 0.8X to 1.69X
Giorgio, your website is delightful!
May I suggest another method for acheiving telecentricity? Find a lens for a mirrorless system that advertises image-side telecentricity, and reverse it either on extension tubes or any tube lens, with no added apertures anywhere. Depending on the chosen lenses, this can give extremely high quality and cover more than full frame. Depending on the EA, you may need to consider adding a flat optical window in front of the whole system, to mimic the missing sensor filter that the reverses lens was designed for.
May I suggest another method for acheiving telecentricity? Find a lens for a mirrorless system that advertises image-side telecentricity, and reverse it either on extension tubes or any tube lens, with no added apertures anywhere. Depending on the chosen lenses, this can give extremely high quality and cover more than full frame. Depending on the EA, you may need to consider adding a flat optical window in front of the whole system, to mimic the missing sensor filter that the reverses lens was designed for.