ollypenrice

Great to see someone just going and doing it!! This is going to be very exciting. Well done that man.

Olly

I have the CF. looks nice and lighter than steel. But lower expansion and all that is a load of rubbish IMO since top and bottom rail are metal and will expand anyway.

I don't gave a reducer yet. Will see how I get on with it natively before trying one of those. Weather has been so rubbish I have yet to properly use it in four weeks so far! I tested plate solving with it last night and it works brilliantly. Then clouded over.....

Steve

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The expansion that matters is between the primary and secondary. My instinct likes the carbon from this point of view but worries about its insulating properties.

It would help if manufacturers would organise their fans properly and have them blowing across the mirror rather than up and down the tube, which is a bit pointless.

Olly

Nothing to be said. That's a very good image indeed. Really super.

Olly

OK, you know that an RC is not optimized for visual because of the enormous secondary. I would also say that it brings other disadvantages once you start AP.

AP is difficult. Starting imaging at long focal lengths makes it more difficult. Your guiding has to be better, the seeing has to be better, there has to be no wind... Imaging at slow F ratios makes it more difficult as well. You need longer exposures (which DSLRs don't like - I guess it is very hot where you live? If so DSLRs will like long exposures a heck of a lot less. A fast F ratio might be essential for you.)

RCs make it more difficult as well. They are tricky to collimate. Not impossible, but the difficulties and obstacles to a nice productive nights are stacking up... These budget GSO RCs are good value but they don't seem to be 'plug and play' instruments. You'll need to fiddle around to get them into shape, or so most people find. This is confirmed by the fact that several outlets are working on versions with the same optics but much better mechanical construction. You stress the import implications and this would make me wonder if an instument with a better QC track record might not be better?

I'd say that for DSLR imaging in the heat Bangla Desh you need a fast F ratio and a shorter focal length would be easier for a beginner.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2277139556&k=FGgG233

Thank you for the comments guys, you are making me blush!

Seriously though what would the equivalent 900mm focal length f/6 triplet refractor set you back?

It doesn't exist. Our TEC 140 with 980mm FL at F7 is about 6000 dollars plus the bits. Your point is well made.

Olly

That M82 is a real stunner. It's great to know that an instrument capable of producing that (in the right hands!) need not cost a fortune. It's very, very impressive.

Olly

Holy smoke, how did I miss this thread?? Incredible stuff, Jesper. Those below you are safe. Are there any huge plantpots menacing you from above???

Olly

We maybe shouldn't call supernovae 'terrible' explosions. They synthesize most of the elements from which we and our environment are made...

(In Smolin's hypothesis they might even have seeded the universe in which we live...)

Olly

Oh wow, bless you Sir! What a feast. I worship Feynman and totally agree with all you've said.

Olly

Good to hear yet another confirmation of the quality of these bins. Your test on Jupiter is my bino benchmark. I've never known the 'cheap and cheerfuls' give anything resembling a clean disk. This kind of aperture and wide field makes for a lovely night out. I get something similar in my little Pronto and Nagler 26. So much to enjoy.

Olly

Tim posted a fabulous image at F10 but I'm just not up for that. Ideally F4 would be my upper limit but life isn't like that! If you take an image at long FL and slow F ratio, but don't get enough data, then you might just as well have used a smaller faster scope because you won't be able to present the slow scope image at full size anyway.

Olly

PS, I should have added that those are great images - and from a scope costing less than a field flattener for a premium apo of simliar focal length!

Ollhy

That's a superb review and covers all the bases fairly.

What we see, yet again, is that the manufacturers are trying to go just a little too cheap. If they increased the price by about 30% I bet they would solve nearly all the problems and the instrument would be fit for purpose and not the starting point for a work in progress, as at present. It isn't surprizing that several firms are working on variants using proper mechanical construction and the original optics, which are clearly good.

And yet another 'dismal Crayford' story. These cheap ones are naff and should be sent back until they stop shipping the useless objects.

It would be good to know how large a chip can be covered using the telecompressor.

As for using them visually, clearly you can. But what possible advantage does the design bring over other Cassegrain variants with similar F ratios, and most notably the Maksutov? Cool down time? Maybe, but the huge central obstruction of the Ritchey Chrétien simply does reduce contrast and that's that. There's no point in railing against it but it is certainly worth pointing out that it gives a decent view if that's the case.

Olly

This is a terrific proposal. Well done to all.

Olly

Real respect means real honesty and there were aspects of Sir PM which made me uncomfortable. However, he was a remarkable man, he created an utterly original media niche and he lived his life as he wished to live it. You can learn a lot of astronomy by reading SIr PM but you can also learn a lot about how to realize your own destiny and how to be yourself. Being yourself is remarkably difficult and Sir Patrick was very good at it. His death is a shock to us all even though his ill health made it something for which we could, in theory, prepare oursleves. I have to say that I don't feel all that well prepared right now.

Olly

This is brilliant information. Many thanks. My own Lunt focuser is useless. I cannot get the slow motion knob to work at all, now, and as Zak says the Feathertouch is total overkill on this instrument.

Again, thanks.

Olly

Ah, a happy thread and fine intervention from Per, there. I love the Feathertouch on my TEC. As stated above it is not the lightest or silkiest action I've felt, it is the most secure and the most precise. That's why it's so darned good.

Olly

Lawks, tell me about it.

Olly

I wouldn't clean too often but actually the coatings are very hard. (That's not an invitiation to go mad, though!!!) One important thing is to use a curved wiping action since curved scratches (God forbid) will not be as visible as straight ones. It is not a lilely scenario but the professionals make a curved action a habit.

Because my stuff works very hard I do have to clean a couple of times a year but I've yet to have a mishap.

Olly

When I de-forked my Lx200 scopes...just loosen one of the fork arms...and the OTA slides out.

The dovetail fits the existing holes - no drilling required.

(The small black "bar" is a safety clamp - which allows you to position and located the OTA on the mount saddle without the fear of it slipping or sliding. Available from Astrodevelopments...their website seems to be down at the moment)

The instrument at the rear ("Ozzie Shiraz" colour) is a Spectra-L200 spectroscope, fitted with an ATik16 guide camera and an ATiK314L imaging camera.

Ah, now my LX200 fork arms were cast in one.

Olly

You use the accessory bolt holes already there. I de-forked an LX200. I found a small car scissor jack helped push the tines apart but don't try it single handed.

Olly

Sub length... well the idea is to get above the read noise with the faintest signal. I've been doing 30 min Ha subs for the first time. What I haven't done, but must do, is a back to back with 15 minute subs to see how theory and practice mesh. You still need a good stack for Sigma to work but Yves and I have a simple policy; 'as long as it takes...'

Olly

The extra focal length of the 11 (even focally reduced) might make life very hard work for DS on anything but a premium mount. I'd check out Damian Peach's website regarding planetary imaging, though. From memory I think he rates them as near equivalent. It's his 14 inch that goes to Barbados.

Olly

Are you sure you want perfect polar alignment? There are two advantages to not having it and one disadvantage. The disadvantage is field rotation in long subs. Agreed. The advantages, though, are that all your dec corrections go the same way so you can disable one of the guide directions and reduce spurious corrections. The other is that you get natural 'dither' - ie you don't use the same pixel on the same bit of sky all night.

Flexure; I'm a sceptic. The only flexure I've ever had was with a dismally ill-designed SX OAG where the whole camera pivoted on the lock screw and needed an external strap to hold it still. Flexure can get you if one of your scopes is a reflector because the mirror can move. But if both scopes are refractors I really struggle to believe that you can't make a nice stiff system. I never see any evidence of flexure in my refractor setups using aggressively tightened ST80s in fixed rings.

I've just received an Altair Astro 60mm finder-guider and I like this becuase it has no focuser, an idea I've long recommended. You just slide the camera nosepiece up and down till you are about right and lock it. Craig Stark says you don't need good focus for guiding. Good enough for me!

I'd drift align till you can get your long subs and then forget it.

Olly

What amazes me about these images is that they look like astrophotos. Mine... well ... didn't! And with that confession I'm outta here to destroy the evidence!

Olly