#41  
Old 17-01-2022, 11:50 PM
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MrB (Simon)
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Hi Lars,
I was refering to the apparent aperature blades in your photo's.
You said all those shots were at f4.
At f4 you should not get this at all.

With regard to the tilt, I bought this lens 6 or 7 years ago.
I got bored with trying to eliminate the tilt with my 645 to EOS and NEX (Sony) adaptors so I have used it exclusively for terrestrial photography ever since.
I may have to revisit astro again with it one day.
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  #42  
Old 18-01-2022, 12:04 AM
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Astrofriend (Lars)
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Hi Simon,
Yes the aperture should be fully open, but it isn't, see my photos through the lens:

http://www.astrofriend.eu/astronomy/...645-300ed.html

Now I have to fix:
The aperture
What's deforme the stars
Tilt problem

Never any boring time when having astronomy as your favorite interest :-) But if I can fix all these problem my Pentax 645 lens will eat all other lenses to breakfast. I don't think it will be too difficult.

/Lars
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  #43  
Old 22-01-2022, 08:03 AM
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Quote:
Originally Posted by MrB View Post
Hi Lars,
I was refering to the apparent aperature blades in your photo's.
You said all those shots were at f4.
At f4 you should not get this at all.

With regard to the tilt, I bought this lens 6 or 7 years ago.
I got bored with trying to eliminate the tilt with my 645 to EOS and NEX (Sony) adaptors so I have used it exclusively for terrestrial photography ever since.
I may have to revisit astro again with it one day.
If you use step down rings instead of the lens's aperture then you don't get those sunstars.

Greg.
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  #44  
Old 22-01-2022, 08:08 AM
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gregbradley
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Quote:
Originally Posted by MrB View Post
Hi Lars,
I was refering to the apparent aperature blades in your photo's.
You said all those shots were at f4.
At f4 you should not get this at all.

With regard to the tilt, I bought this lens 6 or 7 years ago.
I got bored with trying to eliminate the tilt with my 645 to EOS and NEX (Sony) adaptors so I have used it exclusively for terrestrial photography ever since.
I may have to revisit astro again with it one day.
Quote:
Originally Posted by Astrofriend View Post
Hi Simon,
Yes the aperture should be fully open, but it isn't, see my photos through the lens:

http://www.astrofriend.eu/astronomy/...645-300ed.html

Now I have to fix:
The aperture
What's deforme the stars
Tilt problem

Never any boring time when having astronomy as your favorite interest :-) But if I can fix all these problem my Pentax 645 lens will eat all other lenses to breakfast. I don't think it will be too difficult.

/Lars
Use step down rings to get to F5.6.
Your adapter spacing may be a bit off.
Adjust tilt first before working on the spacing as tilt can cause elongated stars but usually only in one corner or side. I use 0.1mm brass sheet and cut it with scissors into smallish pieces that can pack out the offending side.

Greg.
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  #45  
Old 22-01-2022, 08:08 AM
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Astrofriend (Lars)
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Hi,
Now I have attache a spring that force the aperture to be fully open and did some other fix.

http://www.astrofriend.eu/astronomy/...645-300ed.html

I'm up now and taking new astrophotos, for the moment M51, not very big with this lens and it's only 30 degrrees above the horizone for the moment.

/Lars
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  #46  
Old 25-01-2022, 02:10 PM
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Max Vondel (Peter)
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I have had good results with the FF equivalent Pentax SMC-M 300mm F4*
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  #47  
Old 29-01-2022, 12:08 AM
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Astrofriend (Lars)
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Hi Peter,
Pentax has always had a lot of interesting optics. I had a lot of them.

Pentax 500 mm f/4.5
Pentax 135 mm f/2.5
Pentax 50 mm f/1.8

And now the Pentax 645 300 mm ED f/4 medium format.

Nice to hear your 300 mm lens is good for astrophotography.


Since last I have updated my Astroberry systems that control everything. Last update had an update of the auto focuser routine. It looks to do a much better job now (which wasn't bad earlier either).

I have documented what I found for you who find it interesting:
http://www.astrofriend.eu/astronomy/...645-300ed.html

It got a bit slower but I think I can tweak the parameters and get it faster. Just need a clear sky to test it.

/Lars
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