options of a new 700-900ish OTA for imaging

[powerlord]

Hi chaps - equipment in my sig. So I'm sick of the 200p newtonian - it's a big unweildy beast.

So I've got wide up to 430mm covered, then I've got my 9.25x6.7 giving me around 1300mm.

What I don't have is anything in between, other than the newt at 1000mm.

Ideally I'd like something in the 700-900 range, flattened and ready for imaging.

Using with my asi533 and asi1600

Seems to me, looking around I've found two possibilities:

1. a 6" RC and flattener:

https://www.firstlightoptics.com/telescopes-in-stock/stellalyra-6-f9-m-crf-ritchey-chrtien-telescope-ota.html

with a .75 flattener that gives me 1027mmF6.7.. a bit more than I want, but maybe there is a flatter flattener ? 0.6 woudl be ideal ?

coming to 550 quid

OR

1. an svbony 120f7 and

 

https://www.amazon.co.uk/Svbony-Telescope-Achromatic-Dispersion-Astrophotography/dp/B08ZS8PRFX/ref=sr_1_6?keywords=svbony&qid=1639403106&rnid=1642204031&s=electronics&sr=1-6

and 0.8 fattener

giving me 672mm.. but maybe there is a flattener that doesn't reduce ?

coming to around 660 quid.

Or are there some other options ? around that sort of money ?

I'm not sure how keen I am on the RC, as it's still open at the front, and I've found that a right pain to keep clean. However I suspect I'd get clearer imaging with the RC than the svbony with its FL51 glass - though it's all gonna be either NB or OSC+L extreme.

IF I could get a 0.6 flattener for the RC, that would bring it to 822mm, and F5.4 which feels to me ideal. While the svbony is around the same speed, but 672mm.. but  it does have the benefit of less need for collimation, and not open at the front...

thoughts ?

 

[johninderby]

The new Starfield 102 f/7 has fpl 53 glaas so better for imaging but over your budget.

https://www.firstlightoptics.com/telescopes-in-stock/starfield-102mm-f7-ed-doublet-refractor.html

The RC has quite a few users on SGL so someone should be able to give an informed opinion.

Edited December 13, 2021 by johninderby

[vlaiv]

Not sure that you'll find suitable scope in your budget.

For refractor - I'd look at triplets, and those tend to be expensive.

Probably best one would be this one:

https://www.teleskop-express.de/shop/product_info.php/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-7-Triplet-Apo---2-5--RAP-focuser.html

It is 800mm FL - so you can use standard flattener without reduction, but if you wish - you can use x0.8 FF/FR to get to about 640mm of FL.

RC 6" will not take much more than 0.75 reduction. It has smaller corrected field - about APS-C max (28mm) and when you reduce that to x0.75 - you are already at 21mm - that is diagonal of ASI1600. More reduction than that will only work with ASI533 as it is smaller sensor. Look into CCDT67 for that one - it works at x0.67 - but you can push it even higher than that.

Maybe this scope would suit you best:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p12005_Explore-Scientific-MN-152-f-4-8-Maksutov-Newtonian-Telescope-with-Field-Correction.html

No additional optics needed - it can illuminate larger sensor. Only problem is availability - you'll most likely need to wait few months for it.

[iantaylor2uk]

Why don't you just a 2x Barlow on your shorter focal length scope? Would be a lot cheaper than a new scope.

[ollypenrice]

25 minutes ago, iantaylor2uk said:

Why don't you just a 2x Barlow on your shorter focal length scope? Would be a lot cheaper than a new scope.

Too slow for DS imaging? And unlikely to have either a large enough corrected circle or be free from artifacts like tilt, reflection, etc.

 

34 minutes ago, johninderby said:

The new Starfield 102 f/7 has fpl 53 glaas so better for imaging but over your budget.

https://www.firstlightoptics.com/telescopes-in-stock/starfield-102mm-f7-ed-doublet-refractor.html

The RC has quite a few users on SGL so someone should be able to give an informed opinion.

It has the right numbers and it has a rack and pinion focuser. Looks pretty tasty to me, on paper at least.

Olly

[johninderby]

I have the bigger brother of the Starfield 102. The Tecnosky 125/975 F7.8 and it is a great performer. Will be trying some lunar and planetary imaging with it. I’ve found the optics in these scopes are a step better than the SW doiblets with a sharper image with better contrast.

[vlaiv]

That 4" F/7 (or higher) doublets are not completely color free.

I've seen blue halos around stars in OSC images. Either RGB+ L3 from astronomik or NB imaging with those scopes. OSC is not a good option in my opinion (maybe with L3 again as IR/UV cut) - that will tame some of blue bloat.

 

[powerlord]

The svbony 120f7 though.. I throw blue away 9x out of 10 and use the green and red as I am shooting with the L-extreme.

Has anyone got experience of what its like with that ? I was wondering if the FL51 might be good enough for that basically. And as you say, NB. I don't really shoot any RGB stuff tbh, so it would be no great loss ?

I do like the simplicity of refractors - my 72ED is great. @iantaylor2uk as olly says, it would among other things be just waay to slow with a barlow. fine for planetary, but not for DSO.

The MNs are just a bit much, and also big things too - prefer something slightly more compact that the massive newts - I've struggled to get guiding under 1" rms with the newt however I balance it (mental RA spikes now and again 8" or so for some reason).. but with the 9.25 for example I easily get 0.3-0.5 rms with those occasional spikes being 2" or so max)

 

[Clarkey]

What about a smaller F5 150mm newtonian? Much smaller than the 200p but in the right FL range (and cheapish).

[powerlord]

well..still a newt, but not a terrible idea. I see FLO do 2: the sw 150p, and the ts-photon 6" F5.

Any experiences with which is best ? both seem very similar. As it'd be getting fitted with an EAF the DS of the SW isn't any use...

I see the secondary mirror size is in spec for the ts-photon but not the SW.

A smaller newt would certainly do it.. and cheaper too (even with coma corrector).

A good 3kg lighter than the 200p, and a good deal shorter. still don't like open end, but compromises needed somewhere.

stu

Edited December 13, 2021 by powerlord

[Clarkey]

I have the TS F4 which is OK, but I suspect for the F5 version the 150 PDS would probably be a better option. The dual speed focuser is better on the SW and the primary mirror on the TS is open and needs covering for AP.

[powerlord]

primary mirror open on both surely ? I'm probably not understanding you, but they both look pretty much identical.

https://www.firstlightoptics.com/telescopes-in-stock/ts-photon-6-f5-advanced-newtonian-telescope-with-metal-tube.html

https://www.firstlightoptics.com/telescopes-in-stock/skywatcher-explorer-150p-ds-ota.html

 

[barbulo]

I’ve seen good reviews of this 80 APO: https://explorescientificusa.com/collections/apo-triplet/products/ed80-essential-series-air-spaced-triplet-refractor

The flattener is affordable too: https://explorescientificusa.com/collections/flatteners/products/2-field-flattener-lens-for-ed-apo-s

[Clarkey]

3 hours ago, powerlord said:

primary mirror open on both surely ?

Probably not explained very well. There is quite a big gap at the back of the mirror and round the mirror holder on the TS which will let the light in. Not the end of the world but a thought.

[Elp]

130pds? There's a huge SGL thread about imaging with it.

 

[GalaxyGael]

A really well corrected triplet with in built flattener, 103mm aperture at 825 mm focal length is the vixen ax103s. Superb flat field and can be reduced to 635 mmat f/6.16 of you want. 

[powerlord]

So, I talked to FLO and they reckoned the ts-optics 150 probably has the edge over the SW. And at 260 quid seems a steal. Focuser a lot higher quality, which sounds good as the 200p one is pretty agricultural.

They reckon I might not need a coma corrector with the asi1600/533 so I'll try it first and see.

Looks nice too in red and black - will go with my zwo stuff 🤪

So another newt it is.. but a lot smaller one. Will get around to seeing if i can flog the 200p locally in the new year, since this will mean I have 5 OTAs.. which is far too many. Not counting the multitude of DSLR lenses, etc.

thanks for the advice chaps, and I'll post my results of course!

stu

 

[vlaiv]

46 minutes ago, powerlord said:

They reckon I might not need a coma corrector with the asi1600/533

Don't bank on it.

[Clarkey]

On 14/12/2021 at 09:57, powerlord said:

Focuser a lot higher quality

I got the F4 photon with the 'better quality' monorail focuser. I was awful and within a couple of weeks I had replaced it. The F5 I believe has a standard Crayford which may be better.

 

On 14/12/2021 at 09:57, powerlord said:

might not need a coma corrector

As Vlaiv states - don't count on it. However, you will get away with something like a Baader MPCC or similar. I needed to buy the Aplanatic corrector for the F4 despite being told that the MPCC 'should' be OK. I guess it depends how picky you are about round stars.

On 14/12/2021 at 09:57, powerlord said:

this will mean I have 5 OTAs.. which is far too many

Pah. There are never TOO many. Just more than you can use at once😁

[powerlord]

Got today. Was hoping for first light tonight but forecast has changed. Yes it's a Crayford. Had to bodge to fit an EAF to it, one bolt and a cable tie to hold on.. Not ideal but best I could think of. Looks nice. Heck of a lot smaller than the 200p.

Im not a star peeper, so unless there's massive star coma I doubt I'll be bothered. Here my heath Robinson eaf mount

[Clarkey]

Good luck with it. It's surprising how much smaller a 150 is compared with a 200.

I'd be interested to see what the focuser is like. The monorail 'bounced' with small adjustments using the electronic focuser which is why I needed to change it. It would be fine for manual use but it would not work properly using an auto focus routine. I had to bodge a Steeltrack onto the 6" tube. Still better than a sloppy focuser though.

[powerlord]

The old 200p was rack and pinion but OK with it. This seems OK too but more chance of everything hanging from it than the Crayford on the 72ed for example. And with filter wheel, and asi1600 thats a fair amount. But I've tighened it as much as seems reasonable and moved freely with wheel and now no play with EAF connected so hopefully OK.

Will give it a go in daylight tomorrow to find focal point so I'm in roughly right ballpark for first light.

As the back mirror is open might be worth attaching a fan, but can do that later. Not checked collimation yet as waiting for a Cheshire (got an svbony laser but as its really wobbly fit it's pretty useless).

Generally though feels nicely put together for 260 quid. Weird they didn't put knobs on secondary but did put em on primary, but easy to change them when I collimate it. Unlike my celestron I imagine stardard metric I'll have in my spares box.

[powerlord]

 

[Clarkey]

Looks good. I think the Baader will be fine with the f5.👍