The "No EQ" DSO Challenge!

[Nigel G]

6 hours ago, SilverAstro said:

I fear I might have lost the plot here ( long day + some amber nectar!) -
but why do you want to downscale from your 150 reflector to a 130 reflector ? ( going to a refractor is a whole other kettle of fishes ! )
In an Alt-Az context duration of exposure, and number thereof, is the (main?) problem so 150 wins over 130 for photons captured. A secondary problem is the stability of the mount vs. size of scope but you have already proven that is OK for your 150.
Another prob might be the focuser (DS vs not DS) but again you have that sorted !
The 130P-DS (if it is like the 150P-DS) has the secondary closer to the primary for photography at prime focus, but you sorted that with your hacksaw.

Another prob is criticality of collimation at f5 of the fixed 150 vs the adjustable 130, but you sorted that by un-fixing the 150 !

So I am not seeing why you want to go down to a 130 ?

120 refractors are above my paygrade/competance

 

 

I'm not sure really, I think there's big room for improvement without costing hundreds and I'm on the hunt for improvement.   I'm fishing for info, my thoughts were if suggestions were leaning towards refractor then a change over to refractor was the way to go, if reflector then hold on for a while and do the modifications I think mine needs, I would like to keep a 6" rather than a 5" but the only 150 light enough for my mount is the one I have which is far from ideal although it gets fairly good results. The 150pds is 4.9 kg without camerase my camera is 1 kg . My weight  limit  is 5 kg the 120 star travel  and 130p-ds  are both 3.9 kg and within limits with camera  attached 

for now do modifications and keep searching for the bargain. .

Nige. 

[happy-kat]

the weight limits are for observing if you look at eq mounts they have an imaging weight limit often less than half that again. So your mount is doing great given your are using the full weight capability.

[The Admiral]

Nige, I think that your train of thought mirrors my own to some degree (no pun intended!). First things first, I'm lucky enough to own an APO and I'm very pleased with its rendition of stars in my astrophotos. I know that Steve Nickolls owns a Startravel 102 and he struggles with blue bloat, which he freely admits to having.

What keeps coming to my mind, though, is that being limited to short exposures with an Alt-Az mount, I'd like something which has a much greater capacity to hoover up photons, yet with the same sort of focal length (715mm), or may be a bit shorter. But then I come back down to earth, because even if I went from my 4" refractor to a 6" refractor, that is only going to give me just over 2x the number of photons for a given exposure. And a 6" APO is going to be both very expensive and a lot heavier. An alternative would be, say, an 8" (200mm) reflector which would give me about 4x the sensitivity. Now we're cooking, but, an 8" reflector with a ~700mm FL (i.e. f/3.5) is a specialised beast. Cost again, and not to mention sensitivity to poor collimation and fine-ness of focus, i.e. it's going to need special care and attention. Given that I have to drag my gear out each time I want to use it, that's not very practical either. And then all these monsters will be too big/heavy for my existing mount, so then I'd have to look for an alternative mount! Which then raises the question: "EQ or ALT-AZ?"

This is where one sees the merits of an EQ mount, 'cos you can use a small 'scope, like an Esprit 80ED, and just lengthen your exposures, and not worry about field rotation. And then, perhaps, add guiding. Hmm, here we go, costs are beginning to escalate. This is all fine of course, if you have an observatory where you can set everything up and leave it, but for me, in addition to having to set up each time, I can't even see Polaris. We get so few opportunities to get the gear out that I just want to get everything set up with the minimum of fuss. Which is why Alt-Az imaging appeals. But at the end of the day it is going to be a compromise.

I'm not sure if this ramble helps. As the FL of your 150 is a bit longer than the 130P-DS, there probably wouldn't be much difference in the number of photons per pixel, so their sensitivities I guess would be much the same. It seems to me that if you are getting good results from your 150, and you are, why would you want to change? I think it might be a different answer if you were using an EQ mount , mind.

By the way, I like your M31. That's something I've yet to have a good go at, but a bit later in the year I think.

Ian

[The Admiral]

21 minutes ago, happy-kat said:

the weight limits are for observing if you look at eq mounts they have an imaging weight limit often less than half that again. So your mount is doing great given your are using the full weight capability.

I'm not sure if that applies to Alt-Az mounts though. I've seen reports of my Nexstar 6/8 being well over-(theoretical) loaded. Balancing is critical though, I believe, as well as the length of the equipment attached, and of course the mount will suffer a greater rate of wear. Still, I think Nige does well with his gear.

Ian

[SilverAstro]

1 hour ago, The Admiral said:

mirrors my own to some degree (no pun intended!).

The minute you said that I felt sure Nige would second the motion when we put this to the committee

 

3 hours ago, Nigel G said:

 room for improvement without costing hundreds and I'm on the hunt for improvement.

Ah yes I see, note that I have cut out "big", on the grounds that your results are already amazingly impressive !

So, mindful of your desires and knowing of your mechanical skills and expertise with a lathe, how about a Field Derotator ?

[SilverAstro]

43 minutes ago, SilverAstro said:

knowing of your mechanical skills and expertise with a lathe, how about a Field Derotator ?

On second thoughts, a field derotator would probably disqualify for "No Eq" as it is just another means of compensating for the earth's polar motion, an eq mount by another name/philosophy !

[The Admiral]

Hmm, not sure I'd go along with that . It's still using an Alt-Az mount; just an alternative to taking short exposures.

It would be an interesting project, and quite complicated to control as the rotation rate varies according to both azimuth and altitude. Steve sent me this link in a PM; I believe the software provides the control http://www.optecinc.com/astronomy/downloads/altaz_server.htm

Ian

[calli]

10 minutes ago, The Admiral said:

Hmm, not sure I'd go along with that . It's still using an Alt-Az mount; just an alternative to taking short exposures.

It would be an interesting project, and quite complicated to control as the rotation rate varies according to both azimuth and altitude. Steve sent me this link in a PM; I believe the software provides the control http://www.optecinc.com/astronomy/downloads/altaz_server.htm

Ian

Yea, thought about it myself. HOWEVER. ;-) In my opinion it makes no sense. Alt/Az Mounts are often not made for imaging and so you will run into the next roadblock when the resolution/stability fails for exposures which needs a de-rotator. Of course many big a** mounts in obs are Alt/Az but we are talking hobbyist level here. But yes interesting.

Carsten

[The Admiral]

1 minute ago, calli said:

Yea, thought about it myself. HOWEVER. ;-) In my opinion it makes no sense. Alt/Az Mounts are often not made for imaging and so you will run into the next roadblock when the resolution/stability fails for exposures which needs a de-rotator. Of course many big a** mounts in obs are Alt/Az but we are talking hobbyist level here. But yes interesting.

Carsten

Yes I think you are right, I'd sort of forgotten about that limitation! What I've yet to find out though is how much better, if any, the more up-market mounts like the Skywatcher AZ-EQ series or the iEQ45 or the new iOptron AZ PRO GOTO are when used in Alt-Az mode, compared to our more lowly steeds.

Ian

[The Admiral]

On 11/07/2016 at 11:49, Chinapig said:

Hi folks

Just discovered this thread - fascinating stuff, and pretty damn inspiring!  I do have an EQ mount (AZ-EQ6), but often leave it in alt-az mode for purely visual, particularly so I can hang a couple of scopes on it for outreach events.  I've yet to try imaging with it in alt-az, but am now inspired to give it a go.

 

Glad you like it. I think that your pic certainly qualifies

I for one would be very interested in how you'd find your AZ-EQ6 for imaging in Alt-Az mode. With the perception that Alt-Az is only going to be used for visual astronomy, the tracking movements of Alt-Az mounts aren't especially refined. One would hope that the AZ-EQ mounts, being dual purpose, might do better in this regards, but I really don't know if that is true. So any feedback that you can provide would be very welcome. Our humble mounts generally provide a mix of images, some with point-like stars and others showing clear streaking, even taking into account the effect of field rotation. It's just that the tracking is somewhat coarse, and it depends whether an exposure coincides with a particularly jerky movement. The effect worsens with exposure time, and 60 second exposures are pushing it. Please let us know how you get on.

Cheers, Ian

[Nigel G]

Hey guys.

Sorry for not contributing,  my mother has been taken into hospital,  I will catch up on posts later on. But for now I have a mother who needs her son.

Nige.

[The Admiral]

I'm sorry to hear that Nige, I hope all goes well. Mum's are far more important than astronomy!

Ian

[SilverAstro]

echo Ian, and best wishes from me.

[SilverAstro]

3 hours ago, The Admiral said:

Hmm, not sure I'd go along with that . It's still using an Alt-Az mount;

Hmmm I'm not sure I'd go along with myself either ! and I agree with Calli ( I am being very agreeable today, , even though I have just returned from the clutches of the NHS myself   ) that it is a bit ott for amateur alt-az, but from PMs with Nige I know he likes a mechanical challenge 

So, deffo in the experimental challenge category ! Thanks for the link to the software control, I expect Gina could do something with an arduino as well !

Just for curiosity (?!)  an alternative to the complex maths to follow the 'nodding' field rotation motion, that I read about somewhere ( sorry lost link) , is to use an off-axis guide to follow a rotating edge of field star.

Ok, back to reality sorry for the diversion > > >

[The Admiral]

Hmm, that's an interesting way around controlling the field rotation gizmo. But as Calli says, the limitation is going to be the relatively poor quality of tracking provided by the amateur alt-az mounts. If only mount manufacturers would put effort into refining their products to meet this, admitedly somewhat limited, need. Somehow, though, I think we're going to be stuck with what we've got.   One of the problems is that folk tend not to use the more expensive/beefier AZ capable mounts for astrophotography, so we get no feedback as to how good or bad they are in this role. I think it needs a well-healed person to experiment for us 

Ian

[happy-kat]

Hope all turns out well Nige.

Your 8SE mount Ian is at the better end of home altaz mounts I think.

[The Admiral]

Well I think I remain to be convinced of that happy-kat. I do find that quite a few of my subs show streaking, and I limit my sub-length to 30s (convenient because I don't need to use an intervalometer, and most of my imaging is towards the south anyway). Nige seems to get good results from his mount. Perhaps I don't manage to get the best out of it. It does have a decent tripod though.

Ian

[SteveNickolls]

2 hours ago, Nigel G said:

Hey guys.

Sorry for not contributing,  my mother has been taken into hospital,  I will catch up on posts later on. But for now I have a mother who needs her son.

Nige.

Hi Nige,

Sorry to hear about your Mum. Hope she is discharged soon.

Best regards,

Steve

 

[Herzy]

5 hours ago, Nigel G said:

Hey guys.

Sorry for not contributing,  my mother has been taken into hospital,  I will catch up on posts later on. But for now I have a mother who needs her son.

Nige.

Oh, thats awful! I hope she is okay!

 

 

[Stub Mandrel]

6 hours ago, Nigel G said:

Hey guys.

Sorry for not contributing,  my mother has been taken into hospital,  I will catch up on posts later on. But for now I have a mother who needs her son.

Nige.

Best wishes to both of you.

 

[Nigel G]

Thanks for all your well wishes, 

Mum's in for tests after having very bad pains and loosing quite a bit of blood, looks like it's diataviculitus, don't know if I spelt that right but waiting for scan to see the extent of the problem. I am aware of the condition as I  very nearly lost my longest and  bestiist  friend to it a few years back.  Mother has caught this nice and early so fingers crossed.

Thanks again, I will catch up on the posts this evening ☺☺

[Stub Mandrel]

My mother in law has diverticulitis, it took six months to get a diagnosis but she's improving now. I'm sure that the early diagnosis will help ensure things go well.

[madjock72]

Anyone got a cloud remover for the newcastle area.

Anyhow while taking subs doesnt the fact that you take more shorter subs compensate for longer exposures on an EQ mount equal out that problem.?

Edited July 13, 2016 by madjock72

[The Admiral]

On 12/07/2016 at 08:28, Nigel G said:

I'm fishing for info...

Thinking a bit more about this, probably the biggest improvement might be in the form of a focal reducer. I bought a 0.79x reducer for my refractor so that I can image larger scale objects, as I always have to crop off the outer parts of an image because of field rotation. I've not had a lot of opportunity to use it yet, but I have found it gives higher scores in DSS, presumably because the mount movements impact the image less and therefore the stars are rounder, and of course an object will be that little bit brighter (i.e. more photons per pixel than without using it). The image of M57 I posted on May 29th used the reducer. The only thing is I'm not sure how well they work with Newts, I think I read somewhere that achieving focus might be a problem. Perhaps someone with knowledge on Newts can come in here. I see that there is a coma corrector for the 130P-DS which has a 0.9x reduction, though that's not a lot. I'm not sure how these would reduce coma either, or whether one could be found that would work with your 150p.

Glad to hear that your Mum is making progress.

Ian

[Nigel G]

21 hours ago, SilverAstro said:

 

Ah yes I see, note that I have cut out "big", on the grounds that your results are already amazingly impressive ! Thanks 

So, mindful of your desires and knowing of your mechanical skills and expertise with a lathe, how about a Field Derotator ?

It's something I had thought about but come up with problems,  main one being I cannot fit anything in front of the camera due to having to cut the focuser already. I also looked into making a wedge but that would disqualify for the no eq. However a wedge is possible, but would my synscan work or need reprogramming,  then as people have pointed out you will still be limited by the az capabilities. Guiding would be needed. I do happen to have a guide camera but no scope. But this would put me well over weight for my mount so a no go. 

I think the best way for now is to remove the 1 inch section of draw tube that protrudes into the main tube and be very particular about what subs are kept. I know I can improve some there. Also stop being impatient and focus more on one target rather than getting greedy trying to get 2 or 3 in a night as Happy-kat as already pointed out to me ☺ 

One problem I have with the star discovery is I don't think I could use any filters ( nebula or LP ) because of the modifications.  Correct me if I'm wrong please.