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Refractor for galaxies

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#1 Emanuel

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Posted 13 May 2021 - 04:49 AM

Question: does anyone uses refractors for galaxies?

Im asking because i have the FSQ 106 ED and i was wondering if you can use it for galaxy imaging. I have done it before, with my NikonD5300, but, to have a fairly size and detail on galaxies, i always have to do a huge crop on the image.Even with the 1.6X extender, most of the cases its not enough.

Maybe if i use a specific camera with smaler pixels??confused1.gif


Edited by Emanuel, 13 May 2021 - 04:50 AM.


#2 ericm2016

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Posted 13 May 2021 - 07:09 AM

sure. You can. It depends on focal length. For large galaxies like M31 ,you need even shorter focal length. Use http://stellarium.org/ to plan you photography.
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#3 Spikey131

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Posted 13 May 2021 - 08:30 AM

Last night I toured the Leo galaxies and the Virgo cluster with a 4” refractor side by side with a. C8.  The 4” showed many of the brighter galaxies quite well.  I especially enjoyed the Markanian Chain, where several objects could be observed in the same FOV.  My favorite was the area around the “Eyes Galaxies”.


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#4 Drase

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Posted 13 May 2021 - 10:11 AM

 

Maybe if i use a specific camera with smaler pixels??confused1.gif

Tihs is the solution to image small galaxies with small focal length :) The 183MM has very small pixels, it allow to reach tiny details on galaxies 


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#5 Jared

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Posted 13 May 2021 - 10:31 AM

Because of their limited aperture, refractors are not ideal for imaging or visual observation of galaxies. That said, if you own a refractor as your primary or only scope one must adapt.

Most galaxies are relatively small targets, so you will likely want to crop quite a bit. A camera with small pixels can help eek out as much resolution as your skies and diffraction will allow (at the cost of more perceived noise, so you’ll want lots of integration time; no free lunch).

With the FSQ, something like an ASI183 would be ideal for smaller targets. You’ll still have a reasonable number of pixels after you crop for your subject, and you’ll have gotten all the resolution that you can. That combo (without the extender) will yield just under one arc second per pixel. That should be just about perfect. The diffraction limit of your scope is just over one arc second. Couple that with good to average seeing and good guiding and you should be able to get 2.5” FWHM images which is enough resolution for most of the showcase galaxies.

Edited by Jared, 13 May 2021 - 10:33 AM.

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#6 Emanuel

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Posted 13 May 2021 - 12:14 PM

Thanks guys. And yes, the FSQ is my only scope, so, i have to adapt things. :)



#7 alphatripleplus

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Posted 13 May 2021 - 05:59 PM

Question: does anyone uses refractors for galaxies?

 

Yes, I sometimes use my AT72EDII at 430mm focal length with an ASI290MM, a small pixel (2.9micron) camera, for EAA on some of the larger galaxies. Pixel resolution at 430mm is 1.38 arcsec/pixel:

 

M33; 20 x 15sec

 

M33_f6.0_Light_Stack_20frames_15sec_RS_Bin1_20.5C_gain300_2020-11-12_194259.jpg


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#8 alphatripleplus

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Posted 13 May 2021 - 06:05 PM

A few more examples (smaller than M33):

 

NGC891; 30 x 10sec;

 

NGC891_f6.0_Light_Stack_30frames_10sec_RS_Bin1_0.1C_gain300_2021-02-16_204829.jpg

 

M104; 30 x 10sec

 

M104_f6.0_Light_Stack_30frames_10sec_RS_Bin1_15.8C_gain300_2021-04-11_230951.jpg


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#9 alphatripleplus

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Posted 13 May 2021 - 06:13 PM

Last couple:

 

M74; 24 x 15sec

 

M74_f6.0_Light_Stack_24frames_15sec_RS_Bin1_19.1C_gain300_2020-11-12_203808.jpg

 

 

NGC2403; 36 x 10sec

 

NGC2403_f6.0_Light_Stack_36frames_10sec_RS_Bin1_20.1C_gain300_2021-04-12_222129.jpg


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#10 Emanuel

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Posted 14 May 2021 - 02:31 AM

Errol, that is very nice. I do have two cameras like that, the Qhyccd 5L-II-M and the ZWO 120MM mini . The  5L, im using as a guide camera, the 120 i just got it, together with the Asi air pro. I thought you could not use them for long exposures, but seeing your images, i see that you can. How do you do it? With the "normal" programms that we use, like APT or SGP, or you use the programme that comes with the camera, like EZPlanetary of Qhyccd ?

And if you need color on the images? Filter wheel?



#11 alphatripleplus

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Posted 14 May 2021 - 07:04 AM

I'm not doing traditional astrophotography with the AT72EDII - All the pics shown were from using the camera with an EAA  live stacking program (in this case ASILIve, but SharpCap is also commonly used). This software does processing, alignment  and stacking in real time as the images are captured. Take a look at the EAA Forum, where many people do these type of quick captures - quick and more noisy than traditional imaging.

 

For colour in EAA, you would use a one shot colour camera instead of mono, as post-processing of filtered images with a mono camera would take you into the realm of traditional imaging. Some people do use filters and filter wheels (I have one) and dabble in casual imaging.


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#12 Emanuel

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Posted 14 May 2021 - 07:20 AM

Thanks Errol. Anyway, your images do look nice smile.gif


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