Altair Astro 6” Ritchey Chretien review

[johnrt]

Damn those pics make me want to get into AP...

It's a dark and slippery road, and one that is guaranteed to make you poor!

[kirkster501]

It's a dark and slippery road, and one that is guaranteed to make you poor!

...to say nothing of frustrating you to hell and back with our weather!

[Gonzo]

Has anyone thought about replacing the metal tube with a carbon one on this 6" RC?

[kirkster501]

I have a carbon RC8 version - 8 inch. Very nice. I don't think you can "replace" the tube though. You buy it as a CF or Alu. Not sure the 6 inch one comes as a CF though I will stand corrected.

[ollypenrice]

Carbon is stiffer and doesn't expand/contract to affect focus. But it traps heat in the tube more effectively.

Olly

[johnrt]

Has anyone thought about replacing the metal tube with a carbon one on this 6" RC?

What is your reasoning for this, minimise weight, stiffen tube?

[kirkster501]

The carbon tube model has metal upper and lower losmandy and vixen bars making any claims that the carbon fibre model has better expansion characteristics questionable. However I can attest to how light it is!

Sent from my iPhone using Tapatalk

[Gonzo]

What is your reasoning for this, minimise weight, stiffen tube?

It's weight saving mainly.

[tonedeaf]

one moment i looked at the RC10 difference in weight...

please correct me...the weight diff is around 0,5kg!

so for an 15kg OTA thats about 3%

so i would say the weigt is not an issue in this case....

the only thing i can think of is the thermic insulation and the heat contraction.

the heat contraction in combination with the alu-bars (cause they contract) is pointless...

on the other hand the insulation seems to have it´s pros and cons...

but the biggest con i´ve heard of are the baffles....

where heat "pockets" build up and can give some "seeing" issues...

http://www.nightsky.at/Art/8inch_GSO_RC/

(sorry this link is in german, but he describes the problem with the baffles, also heard from this from my local dealer who uses a RC10)

[Gonzo]

You're wright about the weight saving, comparing the 8" and 10" alu V carbon, the weight difference is not that big. You do pay however a premium for carbon.

[Jessun]

I think it's actually steel, rather than aluminium. (A fridge magnet test suggests that to me anyway). That is good news though as steel expands about half as much as aluminium.

The dovetails are aluminium though so that will put some stress on the system unless one end is allowed to slide as in more expensive systems.

I put two Losmandy bars on my steel 8"RC, with the idea that the differences in expansion would at least be symmetrical, and not cause some sort of collimation drift.

/Jesper

[johnrt]

So it would seem there is also a third area to check if you choose a 6" RC on top of the primary mirror & focuser.

I had the OTA in bits again the other day as I still saw some (although much reduced) drift in the fov over time, despite the tightening up of the primary mirror. I removed the front cell and discovered that the secondary mirror also needs checking as it was loose in it's holder, it is again a simple fix, just tighten up the compression ring, re-assemble and check the collimation.

[kirkster501]

Wonder if these issues are unique to the 6" version John? My Carbon Fibre RC8 *seems* OK. That said, I have not been as exactlng as you (yet)......

[johnrt]

Wonder if these issues are unique to the 6" version John? My Carbon Fibre RC8 *seems* OK. That said, I have not been as exactlng as you (yet)......

Only one way to find out!

I also found the primary mirror had a bevelled edge to it, cut at about 45 degrees, and with a textured silver & shiny finish, there were also fines of silver material floating about. I took this opportunity of having the scope in bits to get rid of the excess material and blacken the bevelled edge with a sharpie. Reflective surfaces inside the OTA bar the face of the primary and secondary aren't going to help anything.

Edited July 19, 2013 by johnrt

[kirkster501]

Whats is like to collimate after having the thing in bits?

[johnrt]

Whats is like to collimate after having the thing in bits?

Very easy, primary needed no adjustment whatsoever and the secondary just a tweak.

[kirkster501]

So was this by removing the rear mirror cell from the OTA leaving the front spider assembly with the secondary still within the scope?

[johnrt]

So was this by removing the rear mirror cell from the OTA leaving the front spider assembly with the secondary still within the scope?

No I removed both, the mirror cells are pretty sturdy things even out of the OTA.

[mihaid]

I wish I could stop looking at this thread - But I can't!!

My concerns are two fold - Firstly, collimation and then that in order to really nail it you need to spend probably as much as the 6" in order to get it spot on. Madness!!

If the OP would not mind, what kind of money, ball park figure, would one need to start from zero to acquire images like these, scope is £400 I know. But mounts, dslr, lenses etc. I can't quite get. BTW why this RC is not good for planets? I do have the drive to learn stuff if I can afford it.

[kirkster501]

If I may answer on the behalf of John in terms of collimation which you quote from Sara's post; I am sure he will chime in too. Also he will answer himself regarding imaging stuff etc I also have an 8" version of this scope. Very little is required to collimate a RC design scope. All you need is a Cheshire EP for £25 or so (you may have one from collimating a Newt perhaps?) and also a 2" centre sight piece(£5) - or make one from a film cannister. You can get your scope almost completely spot on with just those and a little patience. All you need is those items and an understanding of the principles involved - which are simple. Break it down into its simplest form; you are tilting two mirrors and the focuser with respect to each other, not splitting the atom...

Edited August 22, 2013 by kirkster501

[johnrt]

I can give you a full list of the equipment I use, but that does not make a definitive list and price. You might get items 2nd hand where I purchased new, you could opt for a different camera, a DSLR for example instead of a mono CCD and filters, Just because I did it this way doesn't make it right, there's more than one way to skin a cat.

Here is a list and approximate cost of the gear I use.

Mount : HEQ5 Pro Synscan £760

Imaging Scope : Altair Astro 6" RC £400

Guide Scope : Skywatcher ST80 £90

Imaging camera : Atik 314l+ £1100

Guide camera : QHY5 £199

Light Pollution filter : IDAS LP2 £170

Reducer : CCDT67 telecompressor £180

Filterwheel & LRGB filters : £300

Pixinsight software : £180

PHD software : FREEEE!!!!

And more recently I've also upgraded to a 3nm Ha filter too - £359

[mihaid]

Hopefully your wife does not get access to this forum.

On a serious note, that is an impressive, expensive for me, list. I was hoping that slapping a dslr onto the 6" RC could achieve similar results. Perhaps it's still best advice to start by visiting the Astro society to get an idea. Do you, have you attended one in your=mine neighbourhood?

[kirkster501]

There is nothing inexpensive about Deep Sky astrophotography regrettably. I shelled out over £2500 - my performance bonus paid in June - for my CCD and filter wheel/filters. I have nigh on £5k worth of gear now. And still not got all what I need. You can easily double or triple that sum for top range gear like a Takahashi scope and Mesu mount with a Atik 11000 - all stuff Olly has btw !

Don't give up on a DSLR. You can get fabulous results with one. Best beginner combination to get good resultsfor DSO AP is a ED80/HEQ5 and a modded DSLR. You can pick that lot up for a grand or so and will get you going.

[Magnum]

Hi John Great right up and great images.

Im just about ready to press buy at this point, though I have one question for you first, do you have to use any form of dew prevention with this scope?

I currently image with refractors and an SCT all with dew bands around the front element which keep them dry even on the dampest night, but I used to use a newt and on very damp nights the primary would dew over so I'm wondering if you have experienced this with the RC, and if so how you deal with it?

I could put a dew band around the bottom of the tube but I'm not sure how effective that would be as the mirror is not in contact with the tube.

Lee

[r3i]

Hi John Great right up and great images.

Im just about ready to press buy at this point, though I have one question for you first, do you have to use any form of dew prevention with this scope?

I currently image with refractors and an SCT all with dew bands around the front element which keep them dry even on the dampest night, but I used to use a newt and on very damp nights the primary would dew over so I'm wondering if you have experienced this with the RC, and if so how you deal with it?

I could put a dew band around the bottom of the tube but I'm not sure how effective that would be as the mirror is not in contact with the tube.

Lee

Whilst the RC isn't as susceptible to dewing as the corrector on an SCT, they do dew up eventually on damp nights.

I've wrapped a band around the bottom of the tube - it does seem to help but I take your point that there's a gap between the mirror and the tube wall so it isn't going to be as efficient as one used to warm up an SCT corrector.

I've also got a Kendrick heater on the secondary: http://stargazerslounge.com/topic/123768-gso-8rc-secondary-dew-heater/#entry1337437  Originally I just had a strap wrapped around the secondary: http://stargazerslounge.com/topic/127421-ikharos-ik-rc10cft-10-f8-cf-truss-tube-ritchey-chretien-by-astrophad/#entry1266658 - this increases the already large central obstruction but whether this has a material effect on the imaging, I couldn't say.