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MTO 1000mm f11 mirror lens
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PostPosted: Tue Nov 06, 2012 1:52 am    Post subject: Reply with quote
iangreenhalgh1 wrote:
Impressive.

Let's not get into talking rubbish about 1000mm refractors being better, first of all, they are very rare, second they are very expensive and third they are bloody massive.

So this MTO is rather remarkable, being affordable but excellent.

If you're looking for typical frauenhofer achromatic two-element telescopes they are not very rare and not very expensive. You can find decent ones for less than 100€ used. They are also very light but ultra long (about 1m). Most of them are very sharp and only limited by diffraction but especially the faster ones often have a lot blue/purple CAs while the MTO has no visible CAs at all and is with it's F11 pretty fast for an 1000mm lens. Blue CAs can be handeled with red filter and B/W conversion or with special CA-killer filters.
I also don't think that a cheap refraktor would beat the MTO easily. Maybe a large diameter expensive one with ED glass or APO triplet etc. but not a usual cheap refraktor!


PostPosted: Tue Jul 16, 2013 12:39 am    Post subject: Reply with quote
Hi again attila, in my experience you are probably right about not being good for birding. I used the 10/1000 for a few years and loved it but the shutter speeds and ISO's need to be too high to be used in anything but very bright light.

Having said that I have included a link below to an image I took of a cockatoo with this lens. The conditions for this shot were about as good as it is possible to get for this lens without artificial lighting. It has a light coloured bird in direct very bright sunlight coming in from the side on a plain back ground so it does not show any aperture rings.

http://www.flickr.com/photos/98915894@N06/9297281202/


PostPosted: Tue Jul 16, 2013 4:04 am    Post subject: Reply with quote
Attila wrote:
Misha_M wrote:
Very good!
It's like a real telescope!

Loved the fact you can snipe a street name sign from a kilometer away.


Indeed, probably a real telescope makes better pictures in smaller size, I am not sure I did never try it.
In my experience above 500mm is pretty hopeless with those lenses what I can afford, probably with $$$ lenses too Laughing



I used to own several different telescopes, from a 4" Celestron APO refractor to a 10" Cave research grade Newtonian. I took pics with a few of them, sometimes using them as long telephoto lenses, sometimes with astrophotography subjects in mind. Most of the terrestrial pics I took, I was just farting around, seeing what sort of resolution I could get out of the scopes. It was actually pretty good.

Most high quality telescopes have diffraction limited optics. Quoting from Wikipedia, "An optical system with the ability to produce images with angular resolution as good as the instrument's theoretical limit is said to be diffraction limited." More on that topic here:

http://en.wikipedia.org/wiki/Diffraction-limited_system

Simply put, most telescope optics are as good as they can get -- they're only limited by whatever flaws may have crept into the manufacturing process, which is damned few with the good scopes.

I have some pics I've kept from one day when I was trying out my Celestron 4" APO refractor (1000mm f/10) and my Meade 10" Cat mirror (2540mm f/10). I was shooting B&W film, probably Tri-X, and I was using a Nikon F2 because it had mirror lock up. The images were scanned on my Epson 4990 at a full 4800ppi resolution, but I've reduced them all to 1600 x 1067 for viewing here. If you click on the images you'll see them at the 1600 pixel size. Other than cleaning up a few spots on the images caused by dust on the negatives, I haven't done any PP to the images at all.

Celestron 4" APO (note the birds)


Meade 10" Cat


These very tall power distribution towers run along a long swath of land that happened to be just on the other side of our backyard fence. A christmas tree grower was leasing the land from the power company to grow christmas trees. In the next shot, I was focusing on christmas trees, but you can see the tower that I was taking pics of in the background. It was probably 400 to 500 meters away from where I was set up.


Finally, here's a half-moon shot taken with the Meade 10"


I think all the images are lacking a bit in sharpness and I don't know whether to blame my eyesight or the Epson scanner. I know that even at the maximum scan resolution, the Epson isn't capturing all the sharpness that can be had from a 35mm negative, so that's some of it. And focusing with such extremely long focal lengths, in this case 1000mm and 2540mm, becomes very difficult. The lightest touch sets the image to bouncing around, but yet you have to touch the focusing knob to focus it. It's a tedious process. If I ever get back into this as a hobby, I will invest in a motorized focuser.

Now, here's a bit of info for you, in case you're not tuned into the goings on in the telescope world:

When you're up at those focal lengths, there is really no difference between a telescope and a long lens, except the scope doesn't have an aperture diaphragm. But neither does a mirror lens, so really there's no difference. It's very possible to take good pics with a telescope and no aperture mechanism.

There are many refractor scopes to choose from, of all different sizes and all glass qualities. A good 1000mm APO or ED scope will probably set you back anywhere from $800 to $1,000 and up, depending on the manufacturer. But there's LOTS of used ones around, and often you can pick 'em up at good prices. The main difference between an APO or ED scope and one using regular glass is that the scope with regular glass might have some CA. But these days CA is easy to get rid of in post. So if you can live with a bit of CA, you can pick up a good quality 1000mm refractor for relatively cheap -- like a couple hundred bucks or maybe even less, used. And no, I'm not talking about the cheapo Tasco (and others) pieces of crap you see for sale at WalMart and the like. I'm talking about good quality refractors that might exhibit a bit of CA.

Both Celestron and Meade -- the USA's two best known telescope makers -- have made 1000mm f/11 scopes that were available in a variety of configurations. Most frequently I see them configured as spotting scopes. But all it takes is a camera adapter and a T-mount to convert it into a 1000mm f/11 lens. And these are excellent quality mirrors. If you're patient you can usually find either a Celestron or a Meade 1000mm outfit on eBay for less than $200. Sometimes less than $100, but that doesn't happen very often. They are still quite popular and usually receive a lot of bidding activity, especially the Celestron, known as the "C90." Celestron probably built a million C90s, whereas Meade didn't build nearly as many of its 1000mm mirrors, so the Celestron C90 is better known, and gets more attention. Optically, I would regard them as equivalent. I've owned a C90, but I've never owned a Meade 1000. The C90 I owned was an outstandingly sharp mirror. Meade has a current 90-series model mirror that has a 90mm front objective and a 1250mm focal length. F ratio is 1:13.8, though, so this limits its usefulness as a lens.


PostPosted: Tue Jul 16, 2013 6:24 am    Post subject: Reply with quote
Plenty of power in those lenses.

I noticed you are from Houston USA CoolTouch. Is that near the space centre? If it is, did you ever try using a mirror to phograph the launch?


PostPosted: Tue Jul 16, 2013 4:51 pm    Post subject: Reply with quote
lewes wrote:
Plenty of power in those lenses.

I noticed you are from Houston USA CoolTouch. Is that near the space centre? If it is, did you ever try using a mirror to phograph the launch?


NASA's various facilities are scattered across the US, mostly due to politics. NASA's Johnson Space Center, its astronaut training facility and Mission Control, is located in Houston because LBJ (President Johnson) wanted a NASA presence in Texas. The actual launch facilities are located at Kennedy Space Center in Cape Canaveral, Florida. NASA Jet Propulsion Laboratories (JPL) are located in Pasadena, California. There's also another launch facility at Vandenburg Air Force Base in California and another training facility in Alabama.

So, to answer your question, no I haven't photographed any launches because they don't happen here. It's kinda odd how it works, but that's politics for you. The launch facility at Cape Canaveral has control of the spacecraft or rocket up until the time it is launched. Once it is launched, Mission Control in Houston takes over and runs the flight for the duration.


PostPosted: Tue Jul 16, 2013 11:14 pm    Post subject: Reply with quote
Thanks for clearing that up Michael, I realise now that the map of the USA in my mind is wildly inaccurate and needs to be updated.


PostPosted: Wed Jul 17, 2013 6:31 pm    Post subject: Reply with quote
lewes wrote:
Thanks for clearing that up Michael, I realise now that the map of the USA in my mind is wildly inaccurate and needs to be updated.


No worries -- I'm sure my mental map of Oz is just as deficient. I know approximately where Sidney and Perth are. Any further detail than that, and I need a real map.
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