New OTA

[dawson]

I'm thinking (still) about the next OTA.

 

I like catadioptic scopes; I've never owned a reflector though, and I don't want to pay many millions for a large aperture apochromatic refractor.

 

I'm primarily interested in solar system objects, but I'd like to be able to view and potentially image some DSOs (see other thread about the sizes of DSOs).

 

I like having glass at the front of the scope which holds the secondary in a fixed position (Mak-Cassegrains and SCTs) and to keep snot off the primary; hence I don't think I want a Ritchey Chretiens.

 

But I do like the dual speed Crayford-type focussers, and I'm not an avid fan just having a one speed focus knob on the back of the OTA as exists on my current Mak.

 

If it were a Mak, I think I'd be struggling to 'afford' anything more than a 7" (180mm) as the price seems to rocket above this; the Skywatcher 180mm Mak is about £780 new and 8" and above are then many thousands (unless there are others I've not found and which are good).

 

So it looks like an SCT. There are various 8" ones out there which I could afford, and possibly bigger but I'm not sure how heavy (for my back) anything bigger would be.

 

I also worry about cool down times. What are peoples experience of this if the OTA isn't kept in the house and kept in a cooler non-heated garage (but attached to the house)?

 

There is a 14 month old Celestron Edge HD 8 f/10 for example on ABS (http://www.astrobuysell.com/uk/propview.php?view=68323) for £750 (about £1250 new) but I fancy something a bit slower, f/12-f/15 really so I can get narrower field of views for the solar system objects.

 

So, any bright ideas?

 

I was hoping I'd get some ideas too at the Astronomy Exhibition in a few weeks, but would like to narrow the field down a bit further first.

 

Thanks for any replies.

 

James

 

 

 

[tuckstar]

Have you considered a long focal length achromat. My friend in similar boat but so much cash he's looking at a Tal 100rs. Just a thought..

[dawson]

I had excluded achromatics on the grounds of them not being as good for imaging with the chromatic aberration issues for when I experimented with DSOs and doubles and stuff.

 

But more than happy to think again if this isn't necessarily the case.

 

Thanks though.

 

James

[Guest Wayne]

I find the c8 a little bit heavy. But I have a back problem two. And dew is a problem. But I haven't sorted my dew heaters yet. :-)

[tuckstar]

Long focal length F10+ will reduce C/A so long as its quality ed glass.

I'm prepared to be corrected but...its a case of balancing between visual, AP, planetary and DSO.if you can find one that does all of these id love to know about it. SCT/MAK???

I only have small scopes but I'm still amazed by the planetary views in my little F13 frac compared to my F6 reflector, but the opposite for DSO.

Good luck matey.

[T A WOW]

Ive been looking at these lately.

http://www.moonrakertelescopes.co.uk/index.html

They look very nice. Reviewed in the lastest issue of astronomy now.

They'd be great for planetary.

[Guest CodnorPaul]

8" SCT (or 9.25 even better) all the way James - I get some decent DSO views, not as great as Angus' 12" dob but good none the less, it is manageable with weight, and you can even get your dual speed focuser for it

[Doc]

The Santel MK91 scopes have great reviews they are 9.1" Mak Cass F13 I think.

 

Expensive but I have seen two go on A&B for about £2k.

 

But they are the Bee's Knees, typical Russian scope built like a tank.

 

There is also the Ylena 150mm Mak Cass F14.2 new £1600

[tuckstar]

If you want a small quality refractor, you really can't beat a telementor. If you can find one!!

[dawson]

But i thought all achromatic reflectors suffered with CA, irrespective of what they were made of, as they are still achromaric and apopchromatic.

A suspect a small, fast, 80mm, doublet or triplet would be nice in the future, but i think i'm after the aperture for the time being with a set of slow optics.

I don't want a 150mm mak as i don't feel it is a worthy step up from the 127mm mak, so 180mm or more i feel would be necessary on the mak front.

The russian mak is hellish expensive new, and i would get a second hand one if i found one.

I need to feel the weight of one of these celestron 8" or 9" s-c scopes. Apparently 7kg for the 8" and 10kg for the 9.25" but both are only f/10.

James

[dawson]

Yes the MK91 looks ideal other than the £3000 price tag (i'm guess at that but it looks to be about $4000 US) and alao the 13kg weight (even more reason to get an observatory).

James

[dawson]

And i keep seeing 14" Meade SCTs for £2500! That really would need an observatory, haha.

Jd

[Guest Eddy]

SCT arre highly versatile James, as you say about f10 which is ideal for most things other than dso but you can always pop a reducer on it to make it some like f6

[Doc]

A long focal length achromatic refractor such as F15 should have hardly any CA.

[dawson]

But an f/15 refractor won't have a great deal of aperture so the resolution will be poorer surely?

Jd

[dawson]

Eddy, i mean f/10 is too fast for me really. If my telescopes desires were on the sea saw of fast (f/4) vs slow (f/20), i'd favourer the slower side of things to please my solar system interests, so f/12-15 i suspect.

Jd

[Doc]

Depends what you are looking at F15 on planets and stars shows a lot of details, sucks on DSO's though.

[dawson]

The skywatcher 180mm mak is f/15. A 40mm meade super plossl eye piece in it would allow you to see 102 of the messier objects. .

Maybe it would just be better to think "there is no happy medium" and get an ota at f/20 for solar system stuff AND another ota at f/4 for the larger DSOs....

Jd

[+RonC]

Always an RC ??

[dawson]

The RC i've seen are on the faster side, wider FOV, and i fancy the secondary being fixed behind some glass.

Jd

[Guest Eddy]

The skywatcher 180mm mak is f/15. A 40mm meade super plossl eye piece in it would allow you to see 102 of the messier objects. .

Maybe it would just be better to think "there is no happy medium" and get an ota at f/20 for solar system stuff AND another ota at f/4 for the larger DSOs....

Jd

What makes you think you can see 102 messier objects? I highly doubt it at f15

[dawson]

I use the term "see" lightly, but there is a thread about the size of DSOs in the astro discussions section; i listed all the messier objects by their angular size, and sorted them by this, then used that field of view website to plug in various scopes and eye piece combinations, and apparently the 180 mak with a 40mm EP has a wide enough fov to fit in 102 of the messier objects. I'm not proposing it's the best scope to look at them.

I am coming around to the idea that thee is no happy medium, and its either something fast, OR something slow; to achieve both well needs two OTAs.

I'll get a weekend job to help pay for it all

Jd

[dawson]

I'm going to find out how to get dual speed focussing on the skywatcher 180 mak. If it's possible i'm going to apply for a zero percent interest credit card

Jd

[Teslar]

Your on the right path I would say in looking for two scope. I have a Mak 180 with Baader Steeltrack SCT focuser. I have seen a few DSO's but its a sod to align the tight FOV makes it difficult to get anything on the chip of the camera. Many have struggled with this and invented solutions by fitting RDF's in addition to the existing finder to make aligning easier its also worth removing the supplied vixen dovetail and buying a set if scope rings. This gives much needed stability to the Mak but the 216mm rings required are like rocking horse droppings

Edited May 2, 2013 by Teslar

[dawson]

Ok, thank you. What happens to the original focus knob then when using the crayford? Where do you leave the primary mirror, all the way in or out or in the middle?

Is the scope quite unstable with the dovetail then? Does rhis impact upon visual or inaging or both? And when is any instability noticed, all the time or when focusing etc?

Thanks.

Jd