Quote:
Originally Posted by Astrofriend
Hi Greg,
Thanks for long detailed answer.
It's more the camera hanging on the lens. The camera is atached with an adapter to the lens. Each has some play, and even the lens have a play. Three different places, but I have a spring that press the camera against the lens to help get rid of the play. But even so there is a tilt.
You can see here:
http://www.astrofriend.eu/astronomy/...645-300ed.html
I will try to put in something on one side of the bayonet to find out how much shims I need, maybe steps of 0.1 mm, or ? But I can also 3D-Print something that hold it together with correct angle and have it adjustable.
I think the lens is good enough to spend that time on it. Or wath do you say ?
My plan is to buy a mirrorless medium format camera in the future. Then there isn't so much optics to choose from.
Lars |
Quote:
Originally Posted by Astrofriend
Hi Greg,
My first idea was to purchace a Pentax 67 400 mm ED lens, but more then five times more expensive compare to the Pentax 645 300 mm ED I have. But even worse, the few reviews of it told that it's softer then the 645 lens.
One more clear night and I think I have the tilt problem fixed.
Do you use your Pentax 645 300 ED wide open ? I use mine at f/4 not as sharp as it can be at f/5.6, but with the bad atmospheric condition here it's enough.
Mamiya 67 also have some APO lenses, but difficult to use because the focus mechanics is hold in the camera house. But the quality are fine what I have read, but no astrophoto reviews.
/Lars
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I used it mostly at F5.6. As I recall I got a stop down ring as that does not give the artifacts around brighter stars. It was cheap off ebay.
Richard Crisp used a Pentax 67 400 F4 EDIF so you can look at his images and decide if its ok or not.
The main advantage of these Pentax 67 lenses is the large 88mm backfocus. One of the longest of any lens. That's handy for attaching a camera with a filter wheel. You don't need as much for your DSLR imaging.
You get a better result getting a ZWO or QHY camera than a 400mm lens in my opinion. The smaller pixels and better sensitivity, lower noise will give you better resolution, dynamic range and the ability to shoot narrowband.
An APSc sensor like the ASI2800 is very popular or the 294 for micro 4/3rd sized sensors.
It will give you more magnification than 400mm.
400mm and I would start looking at the many 75mm aperture APOs around that are low cost.
Greg.