153 replies to this topic

[ris242]

Anyone ever thought or tried the Askar 103 with the 0.6x reducer for visual?

 

The reducer seems to be able to unscrew some threaded adapters and at the M68 thread there is 82mm to make up or 99mm from the M84.

This could easily be done in 1-1/4" diagonal mirrors or prisms........and there are some 2" ones that are around 70mm

 

How close does one need to be to the focal plain for visual anyway?

 

Sitting at a FL of 420mm with 4 inches...........5 degree views (14x) with a 30mm 70 degree EP.........seems like an interesting idea.

 

The only thing .........not enough room to bino with my MBII.

 

 

[RichA]

7mm exit pupil means it's right on the edge and in most viewing situations, it's too little magnification (you sacrifice a lot of magnitude grasp)  but it does provide a wide field, depending on the eyepiece.  For the focus position, you need to factor-in the typical length of a 1-1/4" system which is about 55mm from eyepiece rim to the insertion point in the focuser.  However, using an eyepiece depends on the design and focal length of the eyepiece.  Some low-power 1-1/4" eyepiece are built "tall" and can require more in-travel even though the usual thing is that high-power eyepieces generally need a bit more in-travel from a focuser.  Best thing to do, get the eyepiece and map its exact focal point used straight through, then calculate if you have sufficient in-travel for the configuration you want to do.

As for the binoviewer, I presume there are no multiplication devices that would bring the focal plane out far enough to allow its use?  If not, there is always cutting the tube, like TV did to their TV85 to create, the "Bizarro."

Edited by RichA, 23 July 2024 - 10:32 PM.

[Dave Novoselsky]

Interesting idea.  Thinking outside the box for sure.  I plan on following this thread with interest and hope you carry it forward to completion.

[Jon Isaacs]

 

How close does one need to be to the focal plain for visual anyway?

 

 

 

I'm not sure what you mean.  If you want the stars to be in focus, you need to be right on it.

 

What 2 inch diagonals have an optical path length of 70 mm ?

 

Jon

[ris242]

 

What 2 inch diagonals have an optical path length of 70 mm ?

 

Jon

tell me if its wrong......... (it does seem short lol)

 

https://www.baader-p...hs-coating.html

[ris242]

I'm not sure what you mean.  If you want the stars to be in focus, you need to be right on it.

To take an image yes. I'm sure someone was using a TSFLAT2? or something and close enough was good enough?

 

( Space_Race_T.J.?? )  ring any bells?  lol

[CrazyPanda]

tell me if its wrong......... (it does seem short lol)

 

https://www.baader-p...hs-coating.html

If you expand more information, the actual optical length is 85mm.

 

Prisms have shorter optical path lengths than mirrors.

 

But if you're using a reducer to bring the scope to F/4, you don't want to use a prism, you want to use a mirror.

 

A 2" mirror diagonal has an optical path length of ~112mm: https://www.baader-p...lock-clamp.html
 

That said, based on that diagram, if the backfocus distance is 55mm from the focal reducer, assuming you even have enough inward travel left to bring the whole system to focus, the focal reducer correction will likely produce very bad stars once you get through the 112mm light path distance of the diagonal.

Edited by CrazyPanda, 23 July 2024 - 11:20 PM.

[ris242]

As for the binoviewer, I presume there are no multiplication devices that would bring the focal plane out far enough to allow its use?  If not, there is always cutting the tube, like TV did to their TV85 to create, the "Bizarro."

Adding a GPC would probably defeat the purpose of being at 420mm in FL. lol

(I don't have a large ........short scope........ just the 60ED).

 

you cant cut the tube as you are working with the distance from the reducer..........that wouldn't change.

if you are at the M84 thread on the reducer the max you have is 99mm to make up........to the focal plane.

[ABQJeff]

Adding a GPC would probably defeat the purpose of being at 420mm in FL. lol

(I don't have a large ........short scope........ just the 60ED).

 

you cant cut the tube as you are working with the distance from the reducer..........that wouldn't change.

if you are at the M84 thread on the reducer the max you have is 99mm to make up........to the focal plane.

I have played this game.  Took my 102 F/7 triplet with a removable binoviewer section, removed the extension and tried various placement and combinations of 0.5x focal reducers to get maximum focal reduction that could reach focus and have a usable view.  Actually worked somewhat well I got it to operate at ~240mm.  Problem is: image wasn't great across the field (field curvature, deformed shapes at edge, etc.), but it worked.  TSFlat2 cleaned it up a bit (just don't ask how all this get-up star tested!)

 

Benefit of doing this playing around was I found a way to use a combination of 0.5x reducer with my Quark to give me fill disc solar.  Used that set-up for about a month or so but then just punted on the crazy set-up and just went with a 80 F/6 small apo to do the job right.

 

But I was using the cheap 0.5x reducers.  If you have good quality reducers and using in design range could work very well provided you have correct backfocus (that is what i do with my C11 Edge and 0.7xreducer, provides great 2" eyepiece views and with 146mm backfocus has enough for a diagonal).

 

Edit: I found the thread:  https://www.cloudyni...using-reducers/  

 

Post #17 is my results summary

Edited by ABQJeff, 24 July 2024 - 01:30 AM.

[Starlancer]

I have a Askar 103 and the .6 reducer but have only imaged with it.  Maybe when I am out at the Nebraska star party I will give it a try

[Jon Isaacs]

In my mind, a poorman's NP-101 is a 102mm F/5 achro with a TSFLAT2... About $400 new, $200 used. 

 

 

Jon

[topomountain]

In my mind, a poorman's NP-101 is a 102mm F/5 achro with a TSFLAT2... About $400 new, $200 used. 

 

 

 

Jon

so are you sying $200 for a used 100 f5 achro and $200 for the tsflat2?

 

so how close is the poor mans tv101 with the at28 uwa

 

i know with the higher mags its no contest anyway

 

i have a 100 f5 achro and my vixen ed102ss f6.5, and i keep thinking id like a tsflat2

[Jon Isaacs]

 

so how close is the poor mans tv101 with the at28 uwa

 

How much does field curvature bother you? Are sharp stars at the edge of the field important?

 

Jon

[Terra Nova]

If you expand more information, the actual optical length is 85mm.

 

Prisms have shorter optical path lengths than mirrors.

 

But if you're using a reducer to bring the scope to F/4, you don't want to use a prism, you want to use a mirror.

 

A 2" mirror diagonal has an optical path length of ~112mm: https://www.baader-p...lock-clamp.html
 

That said, based on that diagram, if the backfocus distance is 55mm from the focal reducer, assuming you even have enough inward travel left to bring the whole system to focus, the focal reducer correction will likely produce very bad stars once you get through the 112mm light path distance of the diagonal.

You might be able to get close to the OP’s stated goal using the Baader T-2 BBHS Dielectric Mirror Diagonal Body which in itself has a path length of 43mm, a T-2 to 2” nosepiece, and a Baader 2" ClickLock Eyepiece Clamp with T-2 Female Thread which is a low profile eyepiece holder, but you will still have to deal with the lengths of most 2” eyepiece barrels.

[Phillip Creed]

For visual, a good, "Poor Man's 4" Tele Vue" is...a Tele Vue Genesis.

4" f/5 with the same color correction as a 4" f/10 - f/12 achro.  So it'll show a MUCH sharper view on planets vs. a standard 4" f/5 or f/6 achro.  Prices vary considerably but you can find one for a three-digit price.

A 30mm 70° eyepiece (i.e. 30APM-UFF) will comfortably squeeze in 4.2°.

With a flat field.

If you need it.

Clear Skies,

Phil

 

Edited by Phillip Creed, 25 July 2024 - 12:39 PM.

[maniack]

For visual, a good, "Poor Man's 4" Tele Vue" is...a Tele Vue Genesis.

4" f/5 with the same color correction as a 4" f/10 - f/12 achro.  So it'll show a MUCH sharper view on planets vs. a standard 4" f/5 or f/6 achro.  Prices vary considerably but you can find one for a three-digit price.

A 30mm 70° eyepiece (i.e. 30APM-UFF) will comfortably squeeze in 4.2°.

With a flat field.

If you need it.

Clear Skies,

Phil

 

A poor man's Televue 4" in my opinion is the ST102 + TSFLAT2 coupled with a C5 or C6. You end up with 2 small and cheap telescopes that are easy to mount, compared to a single expensive medium-size telescope.

[25585]

A "rich man's" NP101 is the Takahashi FSQ-106.

[Phillip Creed]

A poor man's Televue 4" in my opinion is the ST102 + TSFLAT2 coupled with a C5 or C6. You end up with 2 small and cheap telescopes that are easy to mount, compared to a single expensive medium-size telescope.

Fair point.  An f/5 Genesis can be pricey, but the prices on the f/5 Genesis go all over the place.  Some sellers want >$1,000.  More fortunate buyers can get one <$600 with enough patience, or netting a lower price by buying one in a bundled package and selling off unwanted/unneeded items.

Nonetheless, it is all in one telescope vs. two.  For DSO sweeping, the ST102 or (better yet) the Orion ST120 works great.  The ST120 is almost a "Poor Man's NP127".  Terrible on planets; more purple than a Prince concert.  It's a one-trick pony.  But that one trick -- low power sweeping -- ohhhh, does it do it to glorious perfection under dark skies.  I don't recall a night I had more fun with a cheap telescope than an ST120 at Cherry Springs back in 2009.

Clear Skies,

Phil

 

Edited by Phillip Creed, 25 July 2024 - 03:52 PM.

[ris242]

A "rich man's" NP101 is the Takahashi FSQ-106.

That's never gonna happen. Half the price of a Toyota Yaris. The wife won't allow that. lol

 

The Askar and reducer is 30% the price of the TV........where I can buy it.

It's a triplet and very short.......most of my scopes are long FL.

[Oldfracguy]

tell me if its wrong......... (it does seem short lol)

 

https://www.baader-p...hs-coating.html

The Baader Star Diagonal Manual I have lists an optical path of 85 mm and a Clear Aperture of 44 mm for the 2" Baader Astro Amici-Prism with BBHS Coating Diagonal #2456120.  

[ris242]

The Baader Star Diagonal Manual I have lists an optical path of 85 mm and a Clear Aperture of 44 mm for the 2" Baader Astro Amici-Prism with BBHS Coating Diagonal #2456120.  

I take it the glass path is through the prism (the glass).........but not to the edges or sides of the diagonal?

 

Why do you need to know the glass path?  Eyepieces usually sit on a ledge and wouldn't contact it?

[topomountain]

How much does field curvature bother you? Are sharp stars at the edge of the field important?

 

Jon

let me clarify

 

removing the comparisons in medium and high mags, im asking how close are the views with an st102 with tsflat2 and at28uwa compared with a tv101 with the same at28uwa and diagonal, assuming all spacing etc is spot on

[Phil Cowell]

Not close an achro even with tsflat2 is still an achro. You’re limited because of the inherent optical limitations of a fast achro. 
At best it would be a one trick pony due to CA. If you don’t care about CA hey then it might work for you. As for trying to image with it forget about it

 

let me clarify

 

removing the comparisons in medium and high mags, im asking how close are the views with an st102 with tsflat2 and at28uwa compared with a tv101 with the same at28uwa and diagonal, assuming all spacing etc is spot on

Edited by Phil Cowell, 25 July 2024 - 07:09 PM.

[RichA]

Fair point.  An f/5 Genesis can be pricey, but the prices on the f/5 Genesis go all over the place.  Some sellers want >$1,000.  More fortunate buyers can get one <$600 with enough patience, or netting a lower price by buying one in a bundled package and selling off unwanted/unneeded items.

Nonetheless, it is all in one telescope vs. two.  For DSO sweeping, the ST102 or (better yet) the Orion ST120 works great.  The ST120 is almost a "Poor Man's NP127".  Terrible on planets; more purple than a Prince concert.  It's a one-trick pony.  But that one trick -- low power sweeping -- ohhhh, does it do it to glorious perfection under dark skies.  I don't recall a night I had more fun with a cheap telescope than an ST120 at Cherry Springs back in 2009.

Clear Skies,

Phil

 

I would at least try for an SDF.

[Oldfracguy]

let me clarify

 

removing the comparisons in medium and high mags, im asking how close are the views with an st102 with tsflat2 and at28uwa compared with a tv101 with the same at28uwa and diagonal, assuming all spacing etc is spot on

 

Not close an achro even with tsflat2 is still an achro. You’re limited because of the inherent optical limitations of a fast achro. 
At best it would be a one trick pony due to CA. If you don’t care about CA hey then it might work for you. As for trying to image with it forget about it

Phil is right on.  The TSFLAT2 in a faster 4" (f/5, f/6.5) achromat really only flattens the field by getting rid of most of the inherent field curvature, and, in my experience, is really only useful when going for wide-field, low-power views with better-corrected 2" eyepieces like the 28mm UWA and the 30mm UFF.  Even when I used a TSFLAT2 with an 80mm APO-type refractor, I removed it for high magnification viewing.

 

The difference between using a TSFLAT2 and not using it is pretty remarkable, sort of like looking though an f/4 or f/5 Newtonian with and without a Coma Corrector.  The difference is quite apparent, whether the Newtonian has a custom mirror or a mass-produced one.  With refractors, the TSFLAT2 has an added benefit in APO-like scopes.  The difference between using a TSFLAT2 in an achromat and an ED or APO refractor shows up in the increased sharpness of the stars not just out along the edge of the field of view, but also in the middle.  At first I didn't understand why this would be so, but after looking at the Double Cluster back and forth using an APO-type refractor with the TSFLAT2 installed and removed from the 2" diagonal (same eyepiece, of course), I stopped trying to figure it out.  The stars in the middle of the field, and especially in the outer regions, were sharper with the TSFLAT2 installed.  You would definitely see improvement using a TSFLAT2 in the ST102 and ST120 (I saw it in an AT125EDL even), and also some improvement with the EON 80ED and AT102ED.