Refractor For Galaxy Imaging

[hughgilhespie]

Thinking aloud. I am lucky enough to have a Tak FSQ106ED which gives me a native f/5 and I have the 0.73 reducer which gives me the possibility of f/3.6 for widefield imaging. However, For imaging galaxies a longer focal length seems to be desirable. Just wondering what's available at around 1000 mm focal length and say f/10 to f/8?

I use an ASI1600MM Pro camera so I would be a bit over sampled. At 1000 mm FL my image scale would be about 0.78 arc-seconds per pixel but other people seem to manage with numbers like this.

My mount is an EQ8 so it should cope with a longish refractor and it would be a permanent setup in an observatory.

So, what scope - refractors preferred and what else should I be thinking about?

Regards, Hugh

[kirkster501]

TEC 140.  But then I would say that wouldn't I ? ?

[MARS1960]

If you want cheap and cheerful Hugh, i'm pretty sure there is a SW 120ED on ABS.

Personally i think the newish SW 72ED would make a great portable galaxy scope.

Both obviously only cheapish doublets but they both do a great job.

 

[PhotoGav]

Hugh,

I currently use a Celestron EdgeHD 8" sct for galaxy imaging. I am not suggesting that is what you should be considering, though with a 2032mm focal length it isn't too bad and certainly gets in close!

My interest in your thread is two fold: firstly, I am intrigued to see what people recommend as a long refractor that doesn't break the bank; secondly I am very interested to hear about your experiences with the EQ8. What kind of RMS guiding values do you typically get, and with what equipment? One thought that I have about improving the perfomance of my Edge 8" is to upgrade to a better mount. I currently use an HEQ5, which typically gives me an RMS of about 0.6" - 0.7". My 8" / QSI 683 combo gives me a scale of 0.55"/pixel, which is suboptimal for the guiding ability of my set up. Would an EQ8 give me a better result?!?

Good luck with your search and I hope you have a healthy budget! I have an Esprit 100 and it is excellent, so I reckon the Esprit 150 certainly has to be on the short list...

[swag72]

Large refractor for galaxy imaging? I would suggest a SW Esprit 150........ Steve ( @steppenwolf ) really does produce the goods with his. If I was buying a large refractor that's where I'd put my money. As it stands I didn't put my money there as a fantastic TMB152/1200 LZOS was offered to me second hand. I will never sell this scope, but the chances of finding one (an original TMB that is not an APM version) is remote. 

Esprit 150 for sure  

Now my thoughts on the EQ8 for long focal work is a different matter - But I won't bog down the thread on this!!

[ollypenrice]

46 minutes ago, kirkster501 said:

TEC 140.  But then I would say that wouldn't I ? ?

Heh heh, so would I! However, the Esprit 150s in captivity have been producing very good stuff.

Your guiding RMS in arcseconds needs to be about half (or less) your image scale in arcseconds per pixel otherwise you will not be resolving at the theoretical values of the setup. This simply means that you could use a shorter focal length, have a wider field of view and produce exactly the same level of resolved detail.

At O.78 arcsecs per pixel you need a guide RMS of just under 0.4 arcsecs by rule of thumb and best guess. Our Mesu 200s can deliver this reliably. The sky can't always deliver the seeing to support it, which means we shoot RGB until it bahaves itself.

Will an EQ8 run reliably at 0.4arcsecs? We need the owners to tell us.

Olly

[ollypenrice]

50 minutes ago, PhotoGav said:

 

My interest in your thread is two fold: firstly, I am intrigued to see what people recommend as a long refractor that doesn't break the bank;

Alas, Gav, there I cannot help you and I doubt that anyone can!

lly

[DaveS]

I just note that there is a new-ish TS 152 f/8 triplet €3500.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10776_TS-Optics-PHOTOLINE-152-mm-f-8-Triplet-APO---3-7--RPA-Auszug.html

Not sure of the optical quality.

[Whirlwind]

Have you excluded the option for the extender for the FSQ?  That will give you a focal length of 800mm and with ASI will give you 0.98"/pixel.  0.2"/pixel isn't such a large difference.

If you want more aperture and willing to spend TEC type money then there is also the TOA130 option.

If not a refractor then a C9.25edge with focal reducer (but is an even longer focal length but with more aperture).

Otherwise there is something like the FLT132 which is a bit shorter in F/l = 925mm 

And a bit shorter still is the Vixen AX103S (825mm) but has a built in flattener, but more lightweight as it is only a 4" (and then why not just get the FSQ extender)

The Esprit 150 has already been mentioned.

Of course if you've won the lottery then there is always the Tak CC250 (1247mm at F/5) with built in autofocuser….

[alan4908]

Well I'd like to give another vote for the Esprit 150, having owned one for a little while now, it gives excellent results when used with the appropriate camera.  With my SX Trius 814 I achieve 0.7 arc seconds per pixel which I've found gives excellent detail on galaxy images.  Since I'm into automated imaging and I also wanted the best possible focus, I also upgraded the stock focuser for a Feathertouch.    

Alan

[kirkster501]

Yes @ollypenrice I have heard good things about the Espirit 150 as well.  Nik Szymanek did a good write up:

http://www.opticalvision.co.uk/documents/107.pdf

 

[hughgilhespie]

Thanks to everyone who replied and all the help offered for me to spend loads of dosh! Actually it's all been very helpful. I should have perhaps said in my original post that I am very much just starting out - I haven't actually managed to take a single image yet. Despite now having all the gear working-ish I am still struggling with software. There is so much to learn!! Day dreaming about new telescopes is really just a way of escaping from grim reality!!

A few answers to specific questions.

@photogav - I have very, very little experience with my EQ8 mount I have managed to guide it using PGD2 and I was getting an RMS guiding error of about 0.55 arc-seconds. I was encouraged by that and hopefully that figure may be improved somewhat when I know what I am doing. My imaging scale with the Tak at f/5 is 2.03 "/pixel so the guiding is good enough with that scope. At 1000 mm FL, I would benefit from improved guiding but could probably get away with the current figures.

@swag72 - I think I'm stuck with the EQ8 - Even dreaming of an Esprit 150 is terrifying. To expand the dream to a new mount as well..................

@ollypenrice - Yeah - I can do better than 0.4 "/pixel no problem - at least as long as I keep dreaming!

@kirkster501 - TEC140? - See above reply about fiscal limited dreaming.

Again - thanks to everyone. Now back to trying to get my dome to rotate in glorious sychrony with my telescope.

Regards, Hugh