Go Back   IceInSpace > Equipment > Equipment Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 21-02-2019, 07:03 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Celestron & Meade marriage...

Well, only here in my backyard - I attached new Meade 4000 0.63 FR to C11.
The working distance is not quite right (I have yet to determine is it too long or short), vignetting and out of focus is visible on the attached crops (trapesium in the centre and star in the corner, from the same frame)..

But the difference between "with" and "without" in terms of illumination is pretty huge (well, ~2x... both exposures were 15sec).
All images are single frames, taken at ISO6400.
Weather was OK before clouds rolled in (with rain), all 6 stars in Trapesium were clearly visible, both visually and on photo.
Attached Thumbnails
Click for full-size image (trapesium.jpg)
99.9 KB149 views
Click for full-size image (without_with.jpg)
119.6 KB144 views
Attached Images
 

Last edited by bojan; 21-02-2019 at 11:09 AM.
Reply With Quote
  #2  
Old 21-02-2019, 10:13 PM
Sunfish's Avatar
Sunfish (Ray)
Registered User

Sunfish is offline
 
Join Date: Mar 2018
Location: Wollongong
Posts: 1,792
A shotgun wedding surely.

I purchased an 0.63 reducer for my little C8 for no other reason than field of view at the time and a vague notion that faster was better. I think it was more expensive also. But it has worked all round.

Good to see that it works well on larger SCT. Other than the pain of reflections early on I donít think I take it off. It also seals up the back of the old scope and protects the sensor.

Are there some small DSO targets where it would be better without. .? Perhaps eyepiece projection in that case..?
Reply With Quote
  #3  
Old 22-02-2019, 01:46 PM
raymo
Registered User

raymo is online now
 
Join Date: Sep 2011
Location: margaret river, western australia
Posts: 5,946
Oodles of small planetary nebulae, many of which are quite bright, and
some have interesting structures.
raymo
Reply With Quote
  #4  
Old 22-02-2019, 02:41 PM
Sunfish's Avatar
Sunfish (Ray)
Registered User

Sunfish is offline
 
Join Date: Mar 2018
Location: Wollongong
Posts: 1,792
Thanks Raymo.

I think there are some of those high in the North I can point at when it clears up.

I did find a galaxy above the trees but it was small and faint , particularly with the moon out.

Bright planetary nebulae in particular would stand out.

Quote:
Originally Posted by raymo View Post
Oodles of small planetary nebulae, many of which are quite bright, and
some have interesting structures.
raymo
Reply With Quote
  #5  
Old 22-02-2019, 09:42 PM
redbeard's Avatar
redbeard (Damien)
Registered User

redbeard is offline
 
Join Date: Nov 2010
Location: Adelaide
Posts: 541
Quote:
Originally Posted by bojan View Post
Well, only here in my backyard - I attached new Meade 4000 0.63 FR to C11.
Just for fun I have the opposite, a Meade LX200GPS and a Celestron FR 0.63.

There were a few brands 0.63 focal reducers that were very similar at some stage, Meade, Celestron and a couple of others. I use mine most of the time as faster and wider. Not for planets though. Getting the right location in the imaging train helps a lot. Here is some info I found on the web a while ago and had saved on the HD. I think the site is gone but here is the text.
Cheers, Damien.




********
"
The information on this page page has been gathered from from many sources such as Russel Croman's white paper on proper placement of focal reducer for RC scopes. My purpose is to capture best practices when I find them, and publish them here. Personal web sites come and go, so I don’t want to link to it and not find it at some future date.

The relation between the reduction factor R, the focal length Fr of the reducer and the distance D between the lens and the focal plane is:

R = 1 - D/Fr

The Meade/Celestron F/6.3 reducer has a focal length of about 230 mm. Therefore, the nominal distance between the lens and the CCD focal plane is about D = FR*(1 - R) = 230*(1 - 0.63) = 85 mm. It is only at this distance, that this reducer gives its nominal reduction factor of 0.63x. The design point of the reducer is matched the the type of scope and the focal ratio. If the reducer does not have the right spacing, it changes the reduction factor and starts introducing coma distortion.

The real point being made hear is that there is a correct distance from the CCD focal plane to the center of the Focal Reducer. This is not dependent on focal length of the scope or the aperture of that scope. It is specific to the focal distance of the focal reducer.

SCT scopes can not use image scale calculators commonly found on the Internet because the imaging train is fixed to the back of the scope, and the primary mirror is moved to achieve focus. The primary mirror moves to bring the scope into focus, thus the focal length of the scope actually changes when focusing the scope. A 2000mm focal length scope may actually vary from 2000 to 2250mm focal length over the range of focus. When the focal length changes, the point of focus behind the scope also changes.

There are two very important considerations on the SCT scope, the distance between the focal reducer and the CCD chip and where the focal reducer is placed relative to the back focus point of the scope. The first distance is fixed as calculated using the above formula. The scond calculation says that the focal reducer is placed in front of the focal point of the scope by some measure based on the reduction factor of the reducer. On refractors this is no a big problem, because the whole equipment train changes in unison with the focusing process.

The SCT has unique issues in that the focal length changes when the primary mirror is moved to bring the image in focus. My experience based on measuring the image scale shows a reduction factor closer to 7 when the imaging train is fixed to 85mm on my Celestron C-8 and the focal reducer attached directly to the back of the scope.

The distance between the camera and the reducer needs to be adjusted until the proper image scale is achieved. According to my calculations the focal reducer need to be about 1/2 inch inside the scope to achieve the proper reduction. In order to get the proper reduction I need to push the distance between the reducer and the camera closer to 95mm. The point is, you have to measure to know the proper spacing. The other thing I learned is the focal reducer needs to be as close to the back of the scope as possible to work. This is true for both the C8 and the LX200 10"

The correct distance from the focal reducer to the CCD focal plane based on image scale measurements, was closer to 95mm. My measurements are based on the center of the focal reducer not the leading edge. The center of the Celestron focal reducer is about 11mm from the back edge of the reducer. If the reduction factor is not 6.3, the focal reducer is not placed properly within the imaging train and the scopes focal point.

Placement of Focal Reducer

Y=D/R

The focal reducer must be placed a distance Y in front of the native focal point of the telescope. This distance is simply the ratio of the working distance of the reducer to the reduction factor.



Actual Working Distance

In practice it is difficult to achieve the exact working distance needed to yield the specified reduction factor. Recalling that the reduction factor is just R = 1 - D/Fr, the above equation for Y can be rewritten as:

Y=(Fr*D)/(Fr-D)

For example, here is the calculation of the working distance for my setup:

Working distance is 85 mm with a Fr =231

Then:

Y=(231*85)/(231-85)

Y=134.48

or about 5.29".

Thus the reducer optics must be 5.29" in front of the native focal point of the telescope, according to Celestron the back focus is about 5.25", which puts the reducer in side the scope to place it properly. The distance from the base of the scope cell to the center of the reducer’s optics is about 30mm, which pushes the focal reducer back even further. This offset has to be taken into consideration when calculating the proper position for the focal reducer. A more practical approach may be to place the reducer as close to the back of the scope, set the working distance from the CCD to the focal reducer, measure image scale and keep adjusting unto the proper scale is achieved. In order to get the proper image scale, I actually had to move the CCD focal plane back another 10mm beyond the calculated distance. This is with the focal reducer directly attached tot he rear cell of the C-8.

As the working distance is increased the image size on the CCD chips decreases and vignetting occurs. So it is possible to change the working distance and or reduction factor because of the equipment you are using. There are consequences for not achieving the proper spacing and proper placement of the focal reducer.

"
******


Also:
http://www.astrotarp.com/Focal_Reduc...nsor_Page.html
Reply With Quote
  #6  
Old 22-02-2019, 10:22 PM
Sunfish's Avatar
Sunfish (Ray)
Registered User

Sunfish is offline
 
Join Date: Mar 2018
Location: Wollongong
Posts: 1,792
Thank you for that. Very interesting.

Measuring my celestron visual back with Pentax adaptor it is 60.3 and the same with a Meade Canon t adaptor attached. So I get a focal distance to face of adaptor of 105.76 with a Pentax which corresponds with closely with Astrotarp link but more than your text suggests. It would be troublesome to adjust without cobbling together a bunch of adaptors.
Reply With Quote
  #7  
Old 22-10-2019, 01:13 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
As was obvious on the test image I attached earlier in this thread, my combination has a problem with working distance.
This was partly because of very confusing and non-standardised terminology used by amateurs and equipment suppliers, partly because I was using adapter combination similar (or same) to this one.
The required (maybe?) working distance for Meade series 4000 0.63x focal reducer is ~61mm (for Canon camera), and the one I have has ~68mm total length.

I could not find the variable adapter neither low profile T2-EOS adapter (they are all ~11mm thick), so it occured to me it should be possible to modify one of my existing low profile M42-EOS adapters, by replacing the yellow part with T2 insert from thick adapter.
I need to machine the black insert to mach the yellow insert dimensions.
Will post the result of this operation when I am done.


EDIT:
Another possibility is this adapter... It is not as thin but it may be worth trying.

Last edited by bojan; 22-10-2019 at 04:48 PM.
Reply With Quote
  #8  
Old 22-10-2019, 03:31 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 8,651
Damian,
The reducer also impacts on the final effective f ratio, as does the back focus positioning.
The attached spreadsheet was developed a few years ago to make things easier.
Attached Files
File Type: zip reducers_V2a.zip (6.3 KB, 20 views)
Reply With Quote
  #9  
Old 22-10-2019, 05:23 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Ready for machining...
Attached Thumbnails
Click for full-size image (c_02.jpg)
122.4 KB18 views
Reply With Quote
  #10  
Old 30-10-2019, 06:37 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Finished..
Now I have distance (flange-to-flange) 59mm minimum (it was ~68), and it is variable to some extent.
Now I have to experiment a bit (with shims, spacers..) to optimize the working distance.
Attached Thumbnails
Click for full-size image (DSC_0164.jpg)
199.0 KB15 views
Reply With Quote
  #11  
Old 24-05-2022, 05:53 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
After covid era and my C11 in Mt Pleasant (while I was stuck in Melbourne), I finally fount the time to test various distances (on star field near Proxima).
Images were taken with above mentioned adapter, with 4 mm spacer and standard (11 mm) EOS adapter, so the flange-to-flange distance varied between 59 and 68 mm.

I can't see any significant differences in image quality at corners of APS sensor (it is terrible) and 1/2 way off the centre (so~so) so I'm guessing I will use it only for faint and small objects and crop out the rest.
Are there any good experiences with this FF/FR?
Attached Thumbnails
Click for full-size image (Corner.jpg)
181.8 KB18 views
Click for full-size image (Closer to centre.jpg)
179.5 KB16 views
Click for full-size image (Proxima_c.jpg)
164.0 KB18 views

Last edited by bojan; 25-05-2022 at 06:35 AM.
Reply With Quote
  #12  
Old 25-05-2022, 08:44 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
After having some similar reports (from other forums), it looks like this FF-FR is only useful for small, dim targets, and only with with heavy cropping of everything outside of 1/4 distance from APS centre (so useful field diameter is ~15 mm or less).


I am thinking now about DIY - I have couple of surplus objectives from binoculars (20~25 cm FL, Ý40-Ý50 mm).
Mounting them inside the camera adapter tube should not be the problem.
Reply With Quote
  #13  
Old 25-05-2022, 12:13 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
I stumbled on this discussion when searching..

It occurred to me that my FF/FR was not assembled properly...
Worth to check on first occasion...
Attached Thumbnails
Click for full-size image (c_34.jpg)
63.0 KB7 views
Reply With Quote
  #14  
Old 25-05-2022, 12:50 PM
JA
.....

JA is offline
 
Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 2,661
Hi Bojan,

I have a Celestron reducer one of these....
https://www.bintel.com.au/product/ce...yABEgK6h_D_BwE

You could borrow it if you like to compare with the Meade optics to see if there is any difference. I notice in the details in the link it says...
"Produces a corrected field of 24mm diameter. The back focus is 85mm, from the reducer’s back element to the cameras sensor"


Best
JA
Reply With Quote
  #15  
Old 25-05-2022, 01:50 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Hi JA,

Thank you for the offer, yes, I would really like to try another sample.
I will PM you.

BTW, mine is this one on the link below (I bought it from that mob 3 years ago).
https://agenaastro.com/meade-series-...flattener.html
Reply With Quote
  #16  
Old 25-05-2022, 05:15 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
In order to obtain recommended (by Bintel) 85 mm distance from FF to sensor (with Canon camera) I need to machine 27 mm long spacer, with 2"-24 and M42 threads, to fit it to FF/FR on scope side and M42x1 for M42x14 mm spacer + M42 EOS adapter.
Or, I need this adapter from ebay (bought it just now), plus some M42 extenders...
Attached Thumbnails
Click for full-size image (c_39.jpg)
34.1 KB6 views
Click for full-size image (c_38.jpg)
28.2 KB8 views

Last edited by bojan; 25-05-2022 at 06:19 PM.
Reply With Quote
  #17  
Old 25-05-2022, 09:52 PM
redbeard's Avatar
redbeard (Damien)
Registered User

redbeard is offline
 
Join Date: Nov 2010
Location: Adelaide
Posts: 541
Some comparison shots for you Bojan.

The Orion-CANON and ETA photos were taken when I did not realise the FR needed to be in the correct place.

The Orion-SONY and EAGLE photos were taken with the Celestron 6.3 FR in roughly the rightish place ish.


Sorry bout the resolution.
Attached Thumbnails
Click for full-size image (ETA4.jpg)
156.6 KB13 views
Click for full-size image (Orion-CANON4.jpg)
112.9 KB12 views
Click for full-size image (Orion-SONY4.jpg)
150.3 KB14 views
Click for full-size image (EAGLE4.jpg)
105.4 KB10 views
Reply With Quote
  #18  
Old 26-05-2022, 04:53 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Hi Damien,

Thank you for the photos :-)

The first pair look similar to what I am obtaining now (working distances used for my test here were 103~117 mm (105 is recommended by Meade and some other users, this is what you get using "standard" camera adapter (which is 58 mm long, + T2-> EOS adapter, as shown on attached drawing)).
Do you remember what was your first and "rightish" distance?

Celestron (? Bintel) recommends 85 mm.. 18mm less than I am currently using, huge difference...
Attached Thumbnails
Click for full-size image (c_35.jpg)
33.7 KB4 views

Last edited by bojan; 26-05-2022 at 05:06 AM.
Reply With Quote
  #19  
Old 26-05-2022, 05:50 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
Reading the Agena add for Meade 4000 series FF/FR, they are now recommending 85 mm working distance (backfocus), just as Celestron (Bintel).

Picture of image train on Agena site is misleading and actually plain wrong (attached from their website). It should look more like the second picture (with ~30mm extender, not ~60 mm)


I am pretty sure, 3 years ago (and recently on Agena) suggested value was 105 mm (also mentioned on CN couple of times, even last year).
Attached Thumbnails
Click for full-size image (focal-reducers-guide_5.jpg)
54.9 KB7 views
Click for full-size image (focal-reducers-guide_Corrected.jpg)
47.0 KB5 views

Last edited by bojan; 26-05-2022 at 11:41 AM.
Reply With Quote
  #20  
Old 26-05-2022, 11:00 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,603
With the help of Astrometry.net, I calculated the actual focal reduction (standard SC-T2 camera adapter, backfocus 105~114 mm ) to be 0.589 (F/5.9).
So - next attempt will be with 85 mm backfocus.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 01:11 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Limpet Controller
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
Astronomy and Electronics Centre
Advertisement