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Expectations - ASI290MC + Camera Lenses?

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#1 Rustler46

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Posted 17 February 2020 - 12:15 AM

Thanks to all the wonderful help offered on this forum, I've been able to see some results, and know what to do to improve. So far it has been with my ASI 290MC on a Celestron-11 (f/6.3) or an AT115EDT (f/7) triplet refractor. 

 

The camera's tiny sensor (3.2 X 5.6mm) has me looking forward to shorter, faster optics. The UV/IR-cut filter I ordered will be delivered tomorrow, and it is supposed to be clear for a few nights. So with the star bloat being corrected by excluding unfocused IR, I'm wanting to use the 115mm refractor for a bit wider field. But I recall having two nice Pentax telephoto lenses from the film era:

  • 200mm, f/4.0, 50mm aperture
  • 135mm, f/2.5, 54mm aperture

For both of these I have the adapters to attach to the ZWO camera. The 200mm works quite well for astrophotography, wide open. I have used the 135mm at f/3.5, but it may also do well for EAA wide open. The fields of view given with the camera are as follows:

  • 200mm - 1.60° X 0.92°, this takes in almost the entire "sword" of Orion
  • 135mm - 2.38° X 1.36°, this almost spans Orion's "belt", also the entire Rosette Nebula

With this in mind, I wondering what has been the experience of forum members using such lenses for EAA. Using SkySafari to display the FOV has me excited about the prospects. If I was to dispense with the heavy Celestron-11 and just mount the 115mm refractor with a telephoto lens on top, the views would be expansive. For smaller objects the refractor could be used (with a Barlow if necessary). Not having to mount the C-11 on my permanent pier would make setup a snap. Go-to and tracking would be entirely adequate with the shorter focal lengths.

 

What can I expect? That 135mm lens at f/2.5 would provide bright, wide fields. The 200mm is no slouch at f/4.

 

What's your take on this?

 

Kind Regards,
Russ


Edited by Rustler46, 17 February 2020 - 12:17 AM.


#2 cmooney91

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Posted 17 February 2020 - 06:48 PM

Sounds like a fantastic combo.

 

I've used the IMX290 mono and IMX224 with CCTV C-mount lenses 8mm through 75mm @ <F2 , and I've use the cameras with a 450mm(f.l.) F4 newt. both focal lengths were a lot of fun. I'm sure the 135mm or 200mm would be a blast to use.

 

 

I've been thinking about picking up a vintage 135mm SLR lens off of ebay to try out. let us know how it goes with your lenses. 


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#3 cmooney91

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Posted 19 February 2020 - 07:56 AM

M46 and it's PN is one of my favorites. Great capture. You even got some of the thin sliver of red  on the outer shell. 

 

With the camera lens you should have a wide enough FOV to try sharpcap's polar alignment tool.  It is really awesome.  You get instantaneous feed back(1-2s exposures),  with graphical and numerical guidance on alt and az adjustments. It makes it is easy to get <10arc-sec PA in <5 minutes. Truly a game changer.



#4 Rustler46

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Posted 19 February 2020 - 11:00 PM

Sounds like a fantastic combo.

 

I've used the IMX290 mono and IMX224 with CCTV C-mount lenses 8mm through 75mm @ <F2 , and I've use the cameras with a 450mm(f.l.) F4 newt. both focal lengths were a lot of fun. I'm sure the 135mm or 200mm would be a blast to use.

 

 

I've been thinking about picking up a vintage 135mm SLR lens off of ebay to try out. let us know how it goes with your lenses. 

Thanks for the reply, Corey.

 

I forgot that Monday, 17th of February is a federal holiday (President's Day). So there was no mail delivery. But my UV/IR-cut filter will be available on Tuesday the 18th for use with my refractor or telephoto lenses. While tonight (February 17th) was clear, I was using the most difficult OTA for EAA - the Celestron-11 @ f/6.3. It has a tiny FOV at the 1750 mm focal length, but it doesn't need the UV/IR-cut filter.

 

But before doing any EAA, I worked on touching up the pier mount polar alignment. The Losmandy G-11 has a nice routine for polar alignment called Polar Alignment Correction. After go-to aligning on 5 stars I went to Betelgeuse (which was near the celestial equator and meridian). After centering that star I chose Polar Alignment Correction. The electronics offset the star from the center of the FOV. Then using the mechanical polar axis adjustments (altitude and azimuth) I brought the star back to the center of the FOV. Next I parked the mount at startup position. Then a restart and repeat this process further fine tuned the polar alignment. After 3 iterations of Polar Alignment Correction, the polar alignment was as close as I could get it. This should reduce drift during image capture, especially with periodic error correction turned on.

 

So I made another try on the Crab Nebula. This one is difficult since SharpCap struggles with finding enough alignment stars. But I finally got a useable stack. Next target was M93, an open cluster with lots of bright stars. SharpCap seemed to run well under these conditions. Finally I made a run on  NGC 2438, a planetary nebula in open cluster M46.  (Apologies for previously not including an observing report as required by forum rules.)

 

NGC 2438 49X6-sec C-11- small.jpg

C-11, f/6.3, ASI290MC, 49 X 6 seconds, live stacked with SharpCap

 

Observing Report:

  • Date and time of the observation = 2020 February 17, ~20:00 local time
  • Seeing & transparency conditions (optional) = fair seeing and transparency
  • Name of subject = NGC 2438 (planetary nebula in M46)
  • Software/process used for the “live” capture = SharpCap, 294 seconds via 49 frames
  • Discussion of observations:
    After a go-to M46 (which was too large for the available FOV), I scanned around (with 1-second, high gain integrations) until the planetary nebula came into view as a ghostly disc. Then gain was adjusted to a mid value for the live stack shown. I was mostly focused on getting the hardware and software issues resolved. But the annular form and reddish rim of the annulus were noted as the stack was built.

I hope you enjoy.

 

Best Regards,

Russ


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#5 Rustler46

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Posted 20 February 2020 - 12:14 AM

Thanks to all the wonderful help offered on this forum, I've been able to see some results, and know what to do to improve. So far it has been with my ASI 290MC on a Celestron-11 (f/6.3) or an AT115EDT (f/7) triplet refractor. 

 

The camera's tiny sensor (3.2 X 5.6mm) has me looking forward to shorter, faster optics. The UV/IR-cut filter I ordered will be delivered tomorrow, and it is supposed to be clear for a few nights. So with the star bloat being corrected by excluding unfocused IR, I'm wanting to use the 115mm refractor for a bit wider field. But I recall having two nice Pentax telephoto lenses from the film era:

  • 200mm, f/4.0, 50mm aperture
  • 135mm, f/2.5, 54mm aperture

For both of these I have the adapters to attach to the ZWO camera. The 200mm works quite well for astrophotography, wide open. I have used the 135mm at f/3.5, but it may also do well for EAA wide open. The fields of view given with the camera are as follows:

  • 200mm - 1.60° X 0.92°, this takes in almost the entire "sword" of Orion
  • 135mm - 2.38° X 1.36°, this almost spans Orion's "belt", also the entire Rosette Nebula

With this in mind, I wondering what has been the experience of forum members using such lenses for EAA. Using SkySafari to display the FOV has me excited about the prospects. If I was to dispense with the heavy Celestron-11 and just mount the 115mm refractor with a telephoto lens on top, the views would be expansive. For smaller objects the refractor could be used (with a Barlow if necessary). Not having to mount the C-11 on my permanent pier would make setup a snap. Go-to and tracking would be entirely adequate with the shorter focal lengths.

So I've worked on gathering the equipment needed to use these telephoto lenses for EAA. My full-aperture Hoya UV/IR-cut filter fits both the 200mm and 135mm lenses. Next is finding the adapters I used between the 135mm lens and the ASI290MC camera. This was used to good effect when photographing the 2017 solar eclipse. 

 

Note:

The recently ordered ZWO UV/IR-cut filter is for the camera's 1-1/4 inch nosepiece. This works well for my telescopes. But it can't be used with the camera telephoto lenses.

 

I'm inclined to start with the 200mm lens for EAA. Though its not as fast as the 135mm lens (f/4 vs f/2.5) it gives a bit more zoomed in view. When I see how that works, then the 135mm telephoto would be interesting to explore. I'll let you all know how it turns out.

 

Regards,

Russ


Edited by Rustler46, 20 February 2020 - 12:16 AM.


#6 Rustler46

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Posted 20 February 2020 - 09:16 PM

So I've worked on gathering the equipment needed to use these telephoto lenses for EAA. My full-aperture Hoya UV/IR-cut filter fits both the 200mm and 135mm lenses. Next is finding the adapters I used between the 135mm lens and the ASI290MC camera. This was used to good effect when photographing the 2017 solar eclipse. 

 

Note:

The recently ordered ZWO UV/IR-cut filter is for the camera's 1-1/4 inch nosepiece. This works well for my telescopes. But it can't be used with the camera telephoto lenses.

 

I'm inclined to start with the 200mm lens for EAA. Though its not as fast as the 135mm lens (f/4 vs f/2.5) it gives a bit more zoomed in view. When I see how that works, then the 135mm telephoto would be interesting to explore. I'll let you all know how it turns out.

I found the adapters needed to adapt both telephoto lenses to the ZWO ASI290MC. Here's the setup used for the 135mm f/2.5:

 

Pentax 135-2.5 & ZWO Video camera-00036.jpg

 

For that lens the tube-ring spacing was kind of tight, but it worked. For the 200mm lens the tube-rings line up in better areas on the lens and camera. Both lenses need a stack of 8mm and 16mm extension tubes (used in the film era for closeup photography). These place the camera at the correct spacing for infinity focus on the camera's sensor. Also in this stack is an adapter - Pentax lens M42 screw-mount thread to ASI camera thread. This adapter is seen above right next to the red flange on the camera.

 

In the above photo the dovetail clamp (with Astro-Tech on the side) fits a standard Losmandy style dovetail. I have one of these atop both my C-11 and C-8. It seems a bit of overkill to have a telephoto lens being carried by a C-11. But it works. Eventually I may just attach a telephoto lens atop the AT115EDT refractor, mounted on the G-11 mount (without either of the SCTs). That Losmandy mount is nearing its weight capacity with C-11 + refractor + telephoto lens.

 

I'm looking forward to doing some EAA with the wide FOV of these lenses.

 

Russ


Edited by Rustler46, 21 February 2020 - 03:09 AM.

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#7 Rustler46

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Posted 21 February 2020 - 05:32 PM

Here's the 200mm f/4 telephoto and ASI290MC installed in the tube-rings and dovetail clamp:

 

200mm f-4 - ASI290MC.jpg

 

Now I'm waiting for the next opportunity to do some EAA with this rig.

 

Clear Skies!

Russ

 


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#8 mclewis1

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Posted 24 February 2020 - 10:34 AM

Russ,

 

Nice work. I've been having fun using a few old Minolta lenses 50 and 135mm with my cameras. I tried out an 85mm (sort of a portrait style lens) and really liked that focal length with my small sensor cameras. With the small sensors I can get away with using a 1.25" filter when it's placed fairly close to the sensor (using a sandwich style mounting within the T thread adapters). I also have a big deep red Hoya filter for the lenses as well that has been interesting to try on the big Ha objects (but smaller more specialized true Ha filters work better).

 

My biggest issues has been finding suitable mounting of the whole configuration (got to get some longer bolts for the larger rings I have). 


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#9 Rustler46

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Posted 24 February 2020 - 03:49 PM

Thanks for your encouraging comments, Mark. My camera's tiny (3.2 X 5.6 mm) sensor makes these telephoto lenses useful for many subjects. Recently I've spent a couple of "cloudy nights" exploring which subjects would be suitable for each of my lenses and telescopes. SkySafari is useful for this, since it can display a rectangle overlay representing the field of view given by my ASI290MC camera. So starting with the Caldwell Catalog, I made a spreadsheet showing which lens/telescope is best for each object. It was easy to change the FOV indicator to match the coverage give by each combination.

 

In the past I had found that these old Pentax telephotos give excellent results both on film and digital astrophotography. Since tonight promises to be clear, I'm considering starting with the 200mm f/4 lens riding atop the Celestron-11. I'm leaning toward dispensing with that big OTA for a while and just mounting the AT115EDT triplet refractor on the G-11 mount. This can be used as the mounting point for the telephoto lenses. Also having the wider telescopic FOV (compared to the C-11) will provide a useful range of focal lengths to match whatever subject is of interest -  805mm, 200mm & 135mm. I have found there are few subjects that need the longer focal length of the C-11 (1750mm).

 

I located the hardware to go with mounting the refractor + ASI290MC/telephoto. Here's the G-11 mount ready to accept the refractor, with 200mm f/4 on top:

AT115EDT + Pentax 200mm F4.jpg

 

Dispensing with the Celestron-11 for a while will make for easy setup on my permanent pier. The little refractor is lighter than the big SCT (12 lbs. versus 35 lbs.) -  much easier for me to install. I'm a bit reluctant to forego views with the larger aperture. But I have been pleasantly surprised how EAA allows a much smaller aperture to out-perform a larger one used in the normal eyeball to eyepiece mode. This will also give time for some work needing to be done on the C-11. The corrector plate needs cleaning inside and out. Then I'll replace gaskets for secondary holder and corrector periphery, before reassembling the OTA. This needs to be done in preparation for this year's Mars apparition.

 

So that's where I'm at for now - always plenty of interest.

 

Kind Regards,

Rustler


Edited by Rustler46, 24 February 2020 - 10:01 PM.



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