# 11 Feb, 2018 23:12
Hello all, i have a Pentacon 500 mm http://allphotolenses.com/public/files/optical/7ef8dbf14a0d67f44aa7cba5cdc3d053.png|
When i tryed it,i has chromatic abberation around stars..and not centered..so a real buumer. But i have changed the front lenses as in the picture now..and i have super pinpoint stars. no chromatic abberation, i have a picture of it. i made a photo of the peiades..the double in the midle shows super color.
But now i have huge halos around bright stars…so my question is..are there filters for ?
Or other ways to avoid it ? this is really a super lens now,great for wide field.
# 12 Feb, 2018 08:59
use a narrow luminance filter (Astronomik L3, B&W 486) and stop it down 1 or two steps. That improves image quality. The mechanical problems of the pentacon lenses due to production-tolerances AND due to their high masses and sensibility for mechanical shock are well known. If you try the 300mm F4 you will find it very good also, if you have a good made one.
To get a better Lens hood you can use some plastics, the original hood is a joke and good for nothing.
My solution: Pentacon 500 F 5.6 with Heliopan hoods and my adapter
who has also one …
# 12 Feb, 2018 11:57
oww thanks..that is good info. i shall post a picture tonight . the funny is, the front lens is also 2 elements,the first one..i flipt it and i get super sharp stars,all flat to the edge.|
before if got bigger stars whit alot of CA.. i have also the 300 f4 ,that is a good one.
diagfragma perfect round circle etc.
i will post some later.. thanks
# 12 Feb, 2018 12:05
interesting. It is a petzval design with two doublets, normally the lens is good sharp but contrast is often weak due to the insufficient lens hood and stray light. Would not have come to the idea of flipping the front group …
The color fringing of those ancient lenses is normally caused by the insuffivient correvtion at the blue and red end of the spectrum, so cutting of these ends to a smaller "window" brings those fringes down ans sharpness up. I use the 500mm stopped down to 8 for the animals in the fields, even though focusing the brick is a job …
For astrophotography I have actually no mount I can use it with due to it's massive weight.
# 12 Feb, 2018 13:37
|i only flipped the first lens,the one that is curved on 2 sides,the other one has a flat and a curve,you need to keep that original. ill show you the photo`s,i made some from the pleiades,the double in the center of it,the blue and golden star are perfect..its almost apo quality. thats why i want to get this lens so perfect.. when you see the photo ,you know what i ment.|
# 12 Feb, 2018 20:02
One of my favorite lenses for terrestrial photography, that and a Vivitar Tele 400mm that came from Tokinas facility. But like you I have had issue using both for astrophotography. The 400mm Tele shows triangular stars. Ive modified the lens a bit to focus well past infinity to try to correct the problem but no.|
Anyway I found the lens flipping interesting, there are no issues with the lens since flipping the lens? Does it still focus correctly on terrestrial objects?
# 12 Feb, 2018 20:30
here is a photo when i had the first lens flipped,you cab see the perfect color balance,the blue and golden stars are awesome..even zooming in all the way,they are perfect.|
the halos looks like its not in focus. iff tryed whit extra spacers..to bad.
on my page https://www.astrobin.com/333363/0/?nc=user
# 12 Feb, 2018 23:33
Interesting … Flipping of the lens also changes the „air-lens“ between the front elements. But it affects only the bright stars. |
# 12 Feb, 2018 23:55
Dipl.-Ing. Jörg Wokeryes,the small stars are perfect,the double in the center are great,even at the edge they are round and good colors.
i would love to get this lens perfect. maybe i try the back part tomorrow.
p.s. when in normal state,you see CA around the stars,on the images its real purple.. but now the color balance is spot on.
# 13 Feb, 2018 01:25
|If you look at the scatter pattern throughout the entire field you will notice it looks allot like the convex area of the corrector you flipped. I would say that it is reflecting light within the void that was creates between the two lenses. Thats my guess|
# 13 Feb, 2018 04:55
yes it looks that way. it was the first lens of the front that i flipped. here is the optical path of it. http://allphotolenses.com/lenses/item/c_1363.html
# 13 Feb, 2018 06:15
The question is why? No coating? The effect is massive, much more than expected.|
# 13 Feb, 2018 07:39
Dipl.-Ing. Jörg Wokeryes,no coating. to bad,it would helped alot
# 13 Feb, 2018 07:53
in that case the game is lost in my mind, I have no idea how to avoid this influence … Coating such a lens will cause much more cost as is good …
# 13 Feb, 2018 12:52
Dipl.-Ing. Jörg Wokeryes..to bad i will try tonight with only 1 lens in the front and the 2 in the back. lets see how that goes.
coating would be very expensive,i can buy a triplet apo for less haha
# 13 Feb, 2018 17:13
|As mentioned somewhere above. A CLS, or similar filter might take care of the problem, otherwise I would either flip the lens back over and correct for CA in post processing, or purchase a corrected APO whether that be something like the sigma 400mm, 500mm, or 600mm APO, or a ED APO telescope.|
# 13 Feb, 2018 17:31
JerHetricki tryed the cls.. didnt work. when the lens is in original state..the stars are really bigger,not color balanced etc. thats why i would get this to work.. of course i could buy aa scope..a triplet apo..ts photoline whit 80 mm cost about 800 eur.
but when you look real close,the stars whit the pentacon are super tight,wont see that to much…ill keep trying,
# 13 Feb, 2018 21:29
Do you have a photo of a star field before you flipped the lens? Also if those lenses are not aligned you will experience anomalies that could take shape as a number of different things. I am assuming that is whats wrong with the 400mm Tele I have, unfortunately I have no way to collimate the lens system. It's fine on terrestrial objects, it will even take amazing images of the moon, but stars are a different story.|
A good doublet is just as good as a decent triplet in my personal opinion. Im sure lots of people with more exposure time than me would disagree. If you can get sharp stars you can fix CA easily in Photoshop. Even a generous amount of CA is easy to fix in post processing.
Id really like to see an image of a star field pre modification if you feel like UL one.
# 14 Feb, 2018 08:32
JerHetrickin normal state it is not perfect round..it has flares ..the ca is also on 1 side. itryed to align it..to bad it wont.
this is a photo whit a pentacon 300 f4 alomst the same type of the lens.. it is perfect aligned. https://www.astrobin.com/full/318511/0/?nc=user
# 14 Feb, 2018 09:02
I think it would be the best to send the lens to Görlitz to Olbricht (i look for the postal adress) for alighnment. I sended my lenses there and with the old GDR-lenses the are the best adress I know to service them. The image you posted shows, what also the 500mm should show if perfectly adjusted and calibrated.
# 14 Feb, 2018 09:05
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# 14 Feb, 2018 11:40
Dipl.-Ing. Jörg Wokerok thanks..ill will try to contact them..would be great to get it perfect.
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