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I don't put much stock in refractors and from what I have seen I'm not keen on RH design either. My comments were specific on your statement that size doesn't matter, because it does.
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Jon Rista:
Have you considered a Canon "white" telephoto lens? I used a Canon 600mm f/4 L II lens for years.
@Jon Rista I just looked up that lens and wow! 17 lenses and $13k for a 150mm objective!!
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Try a Schmidt Newtonian telescope. Meade made a 10" that would give you a larger aperture with no diffraction spikes. Has a front corrector plate that also holds the diagonal for the right angle newtonian optical path... There are other vendors besides Meade.
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+3 on the AP305RH. It was my dream scope and then I bought one.
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Alex Nicholas:
How BIG do you need? Like, you know a 10" f/3 is not faster than a 4" f/3? So unless you want the focal length of a 10" f/3 (750mm), size shouldn't really be that big of a deciding factor.
I'd be looking for a Tak FSQ106N with the 0.63 reducer giving you 106mm f/3.9.
thats going to give you speed, sharpness, no spikes, flat field over MASSIVE sensors, way bigger than 35mm sensors...
Right, a 250mm objective (10") at F3.6 (maximum for filters) give 900mm focal length which is 0.86" per pixel on a 3.76u pixel (imx455/imx571/imx533) and is optimally sampled for 1" - 4" seeing.
The imx455 gives 2.29° x 1.53° FOV which can cover the andromeda galaxy. I think with this I can cover a lot of mid-sized/small deep sky targets but still have enough resolution to get good galaxy images as well at F3.6 my exposure times will be as short as possible.
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Tim Ray:
Try a Schmidt Newtonian telescope. Meade made a 10" that would give you a larger aperture with no diffraction spikes. Has a front corrector plate that also holds the diagonal for the right angle newtonian optical path... There are other vendors besides Meade.
@Tim Ray I've looked at the Meade and it looks pretty good: F4, 30lbs and reported good with an APS-C sensor.
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Alex Nicholas:
I'd be looking for a Tak FSQ106N with the 0.63 reducer giving you 106mm f/3.9.
When you find a Tak .63 reducer, or any Tak reducer for the FSQ106N, post it. I have some friends that may like to try one.
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I very much doubt it and I have used said SN. Typically coma is the only field aberration (of significance) and is about 1/2 of an equivalent (aperture/speed) newtonian, which for a 250mm @ f/4 is frankly HUGE.
Here how it performs (right side):
Maksutov-Newtonian telescope (telescope-optics.net) |
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andrea tasselli:
I very much doubt it and I have used said SN. Typically coma is the only field aberration (of significance) and is about 1/2 of an equivalent (aperture/speed) newtonian, which for a 250mm @ f/4 is frankly HUGE.
Here how it performs (right side):
Maksutov-Newtonian telescope (telescope-optics.net)
@andrea tasselli Good god! I thought SN telescopes were supposed to correct for coma. What size in microns do you suppose the black circle is in the spot diagrams?
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andrea tasselli:
Around 5 microns
@andrea tasselli Do you think a typical newtonian coma corrector would work here?
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No, it won't. For that kind of performance you are looking for you need a Maksutov-Newton (or a Houghton but I never heard of one being actively marketed). Or more prosaically of a newton with a meniscus if you can find one around. Or bent vanes in a standard newton.
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andrea tasselli:
I very much doubt it and I have used said SN. Typically coma is the only field aberration (of significance) and is about 1/2 of an equivalent (aperture/speed) newtonian, which for a 250mm @ f/4 is frankly HUGE.
Here how it performs (right side):
Maksutov-Newtonian telescope (telescope-optics.net)
Ah you're right - forget the SN. I'm keeping my MN.
Looks like the OP will just have to wait and dream of the day a big Intes MN emerges for sale. If serious you could let Markus Ludes at APM know you are interested if anyone in the EU is thinking of selling a big mak.
And someone on CN has a 12" f/4.5, wait for the day they part with that (could be a loooong wait)...
Or splash out for a Riccardi-Honders, possibly custom-made. There is an optical engineer in Melbourne who built a Honders for himself, might make one for a price if you asked him VERY nicely; I can give you a link to him.
The snag however with making anything requiring a large corrector though is obtaining the glass; blanks of the requisite optical quality larger than 190mm simply aren't made anymore except as a special order, cost $$$$$$, and can take 2 years to deliver. There is a Schott paper describing the manufacture of the billets used for the Skywatcher MN190 and how long this takes.
Alternatively there are a couple of CN'ers who have saved the last of the blanks from Newport for making big maks, perhaps they could be persuaded to part with one.
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Alex Nicholas:
If you're REALLY keen and your pockets are ridiculously deep. Astro-Physics Ricardi Honders Astrograph. 305mm f/3.8, no spikes, almost refractor level sharpness.
That's a, I won the lottery or retired good (and don't plan to live to 85) purchase.  |
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+1 for the Sky-Watcher MN190 Mak-Newt. I use mine on the EQ6-r, guide at .5 arcsec with an OAG, and have a well-corrected field with my APS-C (BXT does the rest).
1000mm fl
f5.3
No backspacing issues with reducers, etc.
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Alex Nicholas:
How BIG do you need? Like, you know a 10" f/3 is not faster than a 4" f/3? So unless you want the focal length of a 10" f/3 (750mm), size shouldn't really be that big of a deciding factor.
I think you should rewrite what you said there. Because you cannot compare 10" F3 and 4" F3 and call them both the same.
If you are sampling both telescopes at 1"/px (or just sampling them at the same resolution) the bigger telescope will always be better.
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Luka Poropat:
Alex Nicholas:
How BIG do you need? Like, you know a 10" f/3 is not faster than a 4" f/3? So unless you want the focal length of a 10" f/3 (750mm), size shouldn't really be that big of a deciding factor.
I think you should rewrite what you said there. Because you cannot compare 10" F3 and 4" F3 and call them both the same.
If you are sampling both telescopes at 1"/px (or just sampling them at the same resolution) the bigger telescope will be better always.
Critically important information here! ---^
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Wim van Berlo:
Have you considered a Newtonian with custom bent spider vanes? Vanes without straight edges won't give you spikes. Although, anything in the light path will diffract light in some way. "There ain't no such thing as a free lunch."
I am the happy owner of a SkyWatcher 190MN, and I chose this scope because of its focal length and lack of vanes. This scope performs as well as a much more expensive APO.
cs,
Wim
@Wim van Berlo thanks for your reply.
do you have source for the curved spider that would work on a 10” newt? Will it still hold collimation well?
Also, what camera are you using on your MN190? Is it an IMX571 variant ? Could you post an example of a master image in a rich star field? I’d love to see what the stars look like.
i’ve seen a few YouTube people start with a MN190 but all eventually moved to refractors and stopped using the MN190.
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Christopher Dietz:
+1 for the Sky-Watcher MN190 Mak-Newt. I use mine on the EQ6-r, guide at .5 arcsec with an OAG, and have a well-corrected field with my APS-C (BXT does the rest).
1000mm fl
f5.3
No backspacing issues with reducers, etc.
@Christopher Dietz
what camera are you using? Could you post a master file of an image with a rich stat field?
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John Stone:
do you have source for the curved spider that would work on a 10” newt? Will it still hold collimation well?
These seem to be available: 1800 Destiny On Line Store for Curved Vane Spiders (destinycomp.com)
As for what kind of imagery you get you can have a look in my gallery.
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John Stone:
Wim van Berlo:
Have you considered a Newtonian with custom bent spider vanes? Vanes without straight edges won't give you spikes. Although, anything in the light path will diffract light in some way. "There ain't no such thing as a free lunch."
I am the happy owner of a SkyWatcher 190MN, and I chose this scope because of its focal length and lack of vanes. This scope performs as well as a much more expensive APO.
cs,
Wim
@Wim van Berlo thanks for your reply.
do you have source for the curved spider that would work on a 10” newt? Will it still hold collimation well?
Also, what camera are you using on your MN190? Is it an IMX571 variant ? Could you post an example of a master image in a rich star field? I’d love to see what the stars look like.
i’ve seen a few YouTube people start with a MN190 but all eventually moved to refractors and stopped using the MN190.
Most curved spiders are home made. Your concern about collimation is valid, since bent steel blades act as springs. Sn alternative, and this is easy to test, is to create a mask that covers the straight vanes. This (french) site shows the technique. Just scroll down the page. http://serge.bertorello.free.fr/antiaigr/antiaigr.html
Here's a link to a post on stargazer's lounge. https://stargazerslounge.com/topic/286157-diffraction-spike-mask/?do=findComment&comment=3135056
I use an ASI294MM with my MakNewt, a bit smaller than aps-c, and since I mostly image galaxies, I seldom have rich star fields. You can see results here on my astrobin page,
https://www.astrobin.com/users/wimvb/, for example this image https://www.astrobin.com/wa9vhs/B/
I normally try to avoid star removal or star reduction techniques as I don't want to destroy faint fuzzy background galaxies. The only time I have trouble with star shapes, is when the scope hasn't cooled down enough, usually during the first hour of an imaging session.
A swedish youtuber used the 190MN for a while, but he eventually gave up on it, because he travelled with it in his car to a dark site in the middle of winter in Lappland (near or north of the arctic circle). If I hade to shovel 1 m of snow every time I wanted to image with mine, I would swap for a refractor as well. That youtuber also probably had his scope in a warm car, and used it at -25C on a cold mount. A heavy scope on a cold mount is not an ideal imaging solution. The 190MN performs best if you can have it in a permanent setup. I don't think it's heavier than a 130-140 mm APO (to which it sometimes is compared in terms of performance), but it's bulkier, and therefore more difficult to handle. Here you see mine, next to my 150PDS Newtonian. |
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The MN190 should be able to cover the field needed for the ASI2600MC DUO - my Intes MN65 does which is smaller (165mm f/5) - and the stars in the guide sensor are fine for guiding.
The one thing you'll have to be good at is making and using flats to deal with the vignetting off-axis, just as with any Newtonian.
Right now the scope I'd try to pounce on if I ever found one is the TEC or JMI 203mm f/3.5.
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Fast, no spikes, great quality, focal length around 1000mm. I know the solution ;)
+5 inch apo like esprit 120/150, toa 130/150 as twinsetup. Bit pricey but a all those scopes are great, able to smash light on big sensors and reasonable fast if you use them in a twin configuration.
cs
andi
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Fastest spikeless scope
For a small small price of.....
https://astrograph.net/TEC-300VT-7-Terebizh |
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Michael Lev:
Fastest spikeless scope
For a small small price of.....
https://astrograph.net/TEC-300VT-7-Terebizh
Wow! $77k, F1.44 is a little too fast for my filters, otherwise I’d have placed my order by now. ;-)
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7.90
6.05
0.00
6.08
0.00
6.06
0.00
7.33
8.59
1.91
3.81
0.00
