First Light Toscano 8" RC

[derrickf]

I picked up a second hand Toscano a few weeks ago and after getting to understand the mechanics of the scope got it reasonably well colimated. During the decent spell of clear nights we had earlier this month I managed to capture M106. If you look very closely, you can just about make out a hydrogen gas jet, at the left of the galaxy core (a tenuous red filament rising almost vertically). It has only recently been determined that this is actually part of a secondary set of spiral arms; this secondary set of arms was revealed by University of Maryland astronomers by combining images from NASA's Chandra X-ray Observatory, NASA's Spitzer Space Telescope, the European Space Agency's XMM-Newton X-ray observatory, and data obtained almost a decade ago with NASA's Hubble Space Telescope (see image at APOD: 2007 April 11 - The Arms of NGC 4258 )

I'm hoping that we get some more clear nights so I can capture some Images in H-alpha light to bring out the jets more clearly.

Image details:

Toscano 8" RC on Astrophysics Mach1 GOTO

ST-10 XME

L= 12 x 600s, R=G=B=5x600s binned 2x2

Comments welcome

[FraserClarke]

Very nice. Can see the H-alpha filament quite nicely in the full size image

What's the f/ratio on the telescope?

[RobH]

Nice result

You must be very happy with the scope.

Cheers

Rob

[derrickf]

Very nice. Can see the H-alpha filament quite nicely in the full size image

What's the f/ratio on the telescope?

The Toscano is f/9; I would say that the mirrors in this are extremely well figured.

Derrick

[derrickf]

Nice result

You must be very happy with the scope.

Cheers

Rob

Hi Rob,

I'm very pleased with it especially when one considers that it cost me far less than 10% of what I paid for a 12.5" RCOS scope some years ago .

Regards

Derrick

[RobH]

Hi Rob,

I'm very pleased with it especially when one considers that it cost me far less than 10% of what I paid for a 12.5" RCOS scope some years ago .

Regards

Derrick

Yes, I looked at the prices of RCOS scopes and then looked away!!

How does it compare with the RCOS in your opinion?

I have one of the new 10 inch Astrotech RC's on order, which I'm dearly looking forward to getting my hands on

Cheers

Rob

[derrickf]

Rob,

I'll be very interested to learn about your experiences with the Astrotech 10" RC; I'm seriously considering buying one. Are you going for the aluminium tube or the CF/FT focuser version?

From an optical quality perspective I would say the Toscano is a match for any RCOS scope I have used (10" to 24"); mechanically the RCOS scopes are really first rate, precision instruments whereas the Toscano is fairly basic. That said, once I got my head around the thinking behind its construction, collimating the Toscano has been pretty easy and we don't have the massive overnight swings in temperature that make some of the mechanical features of the RC so desirable when installed on a mountain top in New Mexico. I had Brian at Astroparts fabricate a rigid spacer so now focusing is easy and consistent using a Robofocus-equipped Moonlite focuser.

BTW there was a discussion recently on the AP user group where somebody asked Roland about dielectric coating of large mirrors, this was his response:

"Dielectric coatings have several advantages over normal metal coatings. They can be made very high reflectivity over a limited wavelength range and they are very tough, so they can be cleaned without picking up scratches. They also have very low scatter (if applied properly).They have two disadvantages over metal coatings. Since a number of layers must be applied in order to achieve high reflectivity, these layers develop strain and thus can warp a large glass surface, especially at the edge. This becomes a real problem when the diameter is large (such as a primary telescope mirror) and the thickness is relatively small. One can make a tradeoff of somewhat lower reflectivity but less strain by reducing the number of layers. One needs at least 50 layers for >99% reflectivity. The process of applying that many layers is an all-day affair - it is not done quickly and is not cheap. I have heard of cheaper diagonals being sold which have few layers and which subsequently reflect less light. The eye cannot tell by looking at the surface if the reflectivity is 70% or 99.5%, but the difference in the amount of image brightness is substantial.In the case of our Maxbright mirrors, the substrate is only 2.5 inches and the actual aperture is 1.8 inches. Any strain and distortion at the edges is masked out by the body of the diagonal. Furthermore, the thickness ratio of the Maxbright is only 3.6:1, so there is virtually no chance that the glass can be bent or distorted to any appreciable degree by the oxide layers. Furthermore, in actual use, the full image beam for any one star or planet occupies only 1/10 to 1/4 inch of the star diagonal surface, so the actual surface accuracy of that very small area is extremely high (on the order of 1/40 wave P-V), even if the total surface has a slight wavelength error.By contrast, telescope mirrors are much larger and have thickness ratios of 8:1 and larger, so they become very sensitive to the slightest strain on their surfaces. They also use the very edge, which is not masked off, and that is where the most distortion takes place. That is also where the most light is gathered, so one would not want to mask this off to any degree.Finally, it must be asked what is meant by a dielectric coating. Theoretically, a dielectric uses only alternating oxide layers of high and low index, deposited one at a time to a very tight tolerance. Some have used this term to describe a modified aluminum layer which has a few layers of oxide applied for protection from the elements and to increase slightly the reflectivity above the normal 88% of the bare metal. How can you tell if it is truly dielectric or merely aluminum with protective oxide coating? A true dielectric with >99% reflectivity can be seen thru - there will be a small amount of light that passes thru, less than 1% but nevertheless easily seen, even with ordinary light bulb illumination. It will be colored deep violet and will change color toward green as you tilt the substrate. If the mirror has an underlying aluminum layer and a few layers of overcoating, it will be almost totally opaque and you would require the brilliant light of the sun to be able to see any light thru it. It will not change color as you tilt it."

Based on a conversation about the mirrors of the 10" GSO RCs (same as the ATRC) I had with Wolgang at Teleskop Service, it would seem that the GSO mirrors have a very good figure and do not suffer from the distortion that Roland describes.

[Taff]

Hi' That's a great capture nice and clear with you.Mark

[RobH]

Very interesting Derrick, and I'm glad to hear that the mirrors on the AT are good.

I know there are 3 or 4 out on loan for testing in the US, and the reports coming in are very good.

I'm not going for the CF one, as at £1000 more, I think this is too much, and I'd rather spend a bit of time doing some temperature training with robofocus and save the money, plus, the saving in weight isn't an issue as my AP1200 won't even notice it

Cheers

Rob

[peter shah]

a super shot....looks like its going to perform:cool:

[Beyond_Vision]

Thats a fantastic first light I bet you are pleased with that

Regards

Kevin

[moocher]

Super shot Derrick!!!! I only know of one Toscano in the UK and that belongs to my mate Alan. I agree with the construction comments but i`d be happy to own one if thats what there capable off....afterall its the optics that really matter...

Alan:)

[ollypenrice]

Simply outstanding image on all counts. The colour is particularly attractive and varied in the galaxy core. Resoolution looks terrific.

Thanks for the post on coatings. I will have a look at my diagonal when I wake up properly!

Olly

[derrickf]

Super shot Derrick!!!! I only know of one Toscano in the UK and that belongs to my mate Alan. I agree with the construction comments but i`d be happy to own one if thats what there capable off....afterall its the optics that really matter...

Alan:)

Thanks for your comments on the image.

I bought this from a chap in Greece who, I think, originally bought it from Ian King in the UK; he has now got a 10" Toscano. The optics certainly are superb and I'm surprised at the quality of the images from such a small aperture with a large secondary obstruction. Whilst the mechanical construction is not particularly sophisticated it is certainly more than capable of fulfilling its purpose - achieving and holding good collimation.

Regards

Derrick

[derrickf]

Simply outstanding image on all counts. The colour is particularly attractive and varied in the galaxy core. Resoolution looks terrific.

Thanks for the post on coatings. I will have a look at my diagonal when I wake up properly!

Olly

Thanks Ollie, I try very hard to avoid the temptation to use process techniques that result in images glowing with electric blues and incandescent reds routinely offered up by many of the US imagers.

I'm glad you found the quote from Roland Christen (owner of Astrophysics) useful - he is full of useful tips like the one in that quote.

Cheers

Derrick