[Obin Robinson]

I tried out Pentax 67 75mm shift lens on my K-1 about a month ago and that was funny experience - I have not seen such bad IQ for years. f/16 was okayish with no shift and that was about it. No more medium fail lenses for me. Maybe modern 645 lenses are okay but these ancient ones are not.

You must have an example with an off centered lens. I haven't had a problem with mine. When the weather clears up I'll post a few examples.

obin

[MJKoski]

Sure, I am interested. It was a used copy which I returned but they had two others. I will likely go Mirex route with Hasselblad zeiss lenses though.

[Obin Robinson]

Take a look at the Mamiya 80mm f/1.9. That's what KELT North and KELT South uses.

"KELT-South observes about 100,000 stars every time is takes a picture, so our precision has to constantly be exquisite."

KELT North - The Little Telescope That Could
"We use two different lenses with KELT. For the wide-angle survey mode, we use a Mamiya 645 80mm f/1.9 medium-format manual-focus lens with a 42mm aperture. To provide a narrow-angle campaign mode, we use a Mamiya 645 200mm f/2.8 APO manual-focus telephoto lens with a 71mm aperture.

obin

[MJKoski]

Oh yeah...that 80mm 1.9 seems to be the dope. I found 3 used locally. Hard choice against Hasselblad Zeiss lenses.

[Obin Robinson]

Oh yeah...that 80mm 1.9 seems to be the dope. I found 3 used locally. Hard choice against Hasselblad Zeiss lenses.

How much are they going for if you don't mind me asking? I see them for ~$200 to $300 depending on condition. It would be worth getting one in perfect shape.

obin

[MJKoski]

229 - 299 euros here. Thing is, that it seems to be very good optically and with Mirex T/S adapter I would have a solution like Canon 90mm T/S lens I used to operate with adapter and Sony A7R2.

[Obin Robinson]

In my opinion that's not a bad price for a good example of the lens. They have a proven track record in astrophotography.

For what it's worth it should be noted the extreme importance of achieving perfect focus when taking photos of the night sky. The difference between a "good" versus an "excellent" photo can be as little as 10 microns. I read an article a few years back that stated that astrophotography is sensitive to changes of as little as 1/10,000th of an inch anywhere in the imaging train. That's the reason why I have dual speed focusers on all of my astrographs. I also built a special precision focuser for a camera lens I was using just in order to achieve perfect focus for astrophotography.

Here's a great article explaining the critical importance of perfect focus when taking astro photos.


The author used GoldFocus, the same software I use, and a Rigel Stepper Motor to control the focuser on his astrograph. For DSLR photos using a conventional camera lens a follow focus system needs to be employed. There are various automated and manual systems available depending on how much money you want to sink into astrophotography.

I've attached two photos of old setups I used a few years back. These photos were taken in my backyard when we lived in Texas. It gives an insight into the amount of equipment I use for taking astro photos. In the bottom photo the astro camera is not yet attached because I am letting all the equipment acclimate for at least an hour before I even bring out the photo gear out. I bring an 80mm f/5 achromat along in order to serve as a wide field spotting scope. This helps when I am searching for a specific object to image at focal lengths of 900mm or more.

In both photos half of the equipment I'm using was either custom made or heavily modified for my usage. I no longer have any of this gear as I've upgraded to more precision instruments customized over the years. I don't have any photos of my current setups to share but it's pretty much along the same lines as what I have in these photos but just newer.

obin

Attached Images

 

[Obin Robinson]

I just found photos of the precision focusing rig I made a few years back. I used a NEMA 17 stepper motor and the belts came from SDP-SI. The large ring to stabilize the lens is a custom made and anodized billet aluminum. The dovetail is solid billet as well. This was a great setup for wide field astrophotgraphy. I found the only flaw was the light pollution in League City, Texas was so severe that the astrophotos looked washed out. The precision focuser worked great though and I still have these components. I believe the lens is a 135mm f/2.5.

obin