We finally had a clear night in NY, and I took the opportunity once again to try some shots of the gibbous Moon.
The first photo was taken using a D800E mounted on a Questar 3-1/2 inch telescope with an F-mount adapter. Focal length is estimated at approximately 1500 mm at about f/16. To minimize motion blur I had to use relatively high ISO and shoot at shutter speeds over 1/200, even using live view or mirror-up mode. This shot was taken at 1/400, ISO 1600, and cropped to about 70% of the original frame height.
The second shot was taken using a Nikon V1 on the Questar with FT-1 and F-mount adapters, again at about 1500 mm and f/16. With the lighter V1 and electronic shutter the setup was more stable, and I was able to get this shot at ISO 200 and 1/100.
In addition to the greater magnification provided by the telescope, the second photo appears to have slightly higher resolution than images in the "Waxing Moon with V1" thread, taken using a 300 mm f/2.8 VR with a TC-20E III (with physical aperture size similar to the telescope).
As usual, full size photos can be viewed at my Smugmug site.
#1. "RE: Gibbous Moon, 6/19/2013" | In response to Reply # 0
nrothschild Registered since 25th Jul 2004Thu 20-Jun-13 09:26 AM | edited Thu 20-Jun-13 09:27 AM by nrothschild
Very interesting, Gerry!
I did not realize that we had another Questar owner here . I have a '97 Broadband Zerodur Duplex (and a '76 7" w/fork mount).
I have never taken an image with the 3.5" that exceeded anything I can do with my 500/4. And it doesn't matter what I shoot- the moon or tree bark 75 feet distant (avoiding seeing issues).
I came to a very tentative conclusion that "shutter shudder" was the problem, and the shutter speeds are too fast for the "hat trick". And apparently it is a problem even at shutter speeds up around 1/100 - 1/200s or so???. I've never quite understood it.
I know I have good optics because I once star tested it against about a dozen other Questars up near New Hope at a Questar happening. And visually the optics are impeccable.
So it is interesting to see that you are getting essentially the same results. I only have DSLRs and an old Coolpix 995. I've thought about a Nikon 1 to solve this problem.
I take it you have a field model, without an equatorial fork?
my Nikonians gallery.
#2. "RE: Gibbous Moon, 6/19/2013" | In response to Reply # 1
Thu 20-Jun-13 01:39 PM
The Questar 3.5 is an early 1970s standard model w/BB coatings, refurbished in the late 1980s. I have always been happy with the optics, and the resolution of the V1 shot shows that it is still quite good. I agree that shutter shudder is the problem. I always avoided using a tripod with the Questar, if possible, instead using the supplied legs on a solid base, particularly for photography. With the relatively heavy DSLR and the counterweight on the tube the setup is balanced, but responds like a big seesaw to any vibration. Conditions were quite good last night, no wind and relatively good seeing, but the scope/tripod setup was not quite adequate for the D800E shots.
Images with the telescope have significantly lower contrast than those from the lens + TC, most likely due to additional diffraction introduced by the central obstruction, as well as, the higher magnification. Thus more contrast enhancement was applied in PP.
#4. "RE: Gibbous Moon, 6/19/2013" | In response to Reply # 2
nrothschild Registered since 25th Jul 2004Fri 21-Jun-13 06:39 AM
I use an old style Questar Tristand. It is quite stable, but my wedge is the southern 0-70° latitude version. I bought it, used, while preparing for the 1998 solar eclipse in Aruba at 10° latitude.
The problem I have is I am very limited in declination because the curved "arm" of the tristand head limits DSLRs when trying to shoot high declinations. The 0-70° version has a longer arm and therefore is more of a problem although it is not clear to me how much. I think it is a problem even with the standard 26-90° head.
Questar sells an offset wedge to convert my head to a 20-90° range but I never popped the money for it, as they are rather expensive (like all Q accessories). Probably should, it would solve a couple of other problems.
Actually, I should have bought a 20-90° version and the wedge for just that one time adventure but I didn't understand all the implications. Plus, tristands are tough to find used.
If you have a fork mount why did you not use the motor drive to eliminate celestial movement? Just curious.
my Nikonians gallery.
#5. "RE: Gibbous Moon, 6/19/2013" | In response to Reply # 4
Sat 22-Jun-13 02:55 AM
>If you have a fork mount why did you not use the motor drive
>to eliminate celestial movement? Just curious.
Normally, I would have polar aligned the telescope with the supplied legs, and used the drive . This was an impromptu experiment to try the Nikon V1 on the Questar. In order to avoid obstruction from some trees, I had to set up in an awkward location that required the tripod. Since I expected to use shutter speeds high enough to minimize celestial motion, I simply mounted the Questar base directly to the tripod plate, and used the Questar controls for altitude-azimuth orientation. To polar align on the tripod, I would have had to mount the telescope via a ball head, resulting in an unbalanced, and even less stable, configuration. I only decided to try a comparison with the D800E after I had set up.
I did try again last night with the Questar polar aligned using the drive with the supplied legs positioned on the ground. I think that vibration blur was much reduced. However there was so much blur due to moisture and in the atmosphere and thin clouds that I could not get anything even close to the previous night's shot. I did not even try using the V1.
Also, it was instructive watching the effects of bad seeing on the screen of my computer tethered to the D800E in live view (and a lot easier to focus and aim the scope than by crawling on the ground ).
I should really get a better support for the Questar, though the tristand and astropier seem ridiculously overpriced.
#3. "RE: Gibbous Moon, 6/19/2013" | In response to Reply # 0