48 replies to this topic

[Tom Stock]

My understanding is that it is a lemon. These came out for a short period when switching china manufacturers.

Sadly many still exist.

[asanmax]

My understanding is that it is a lemon. These came out for a short period when switching china manufacturers.

Sadly many still exist.

Thank you, I'll try to get in touch with Meade to see what they have to say.

[Tom Stock]

Thank you, I'll try to get in touch with Meade to see what they have to say.

Thats what I would do. The story I heard was that the Chinese manufacturer mistook focal length for radius during manufacture so they are roughly half the expected focal length (maybe in only one of the elements? not sure).

 

I read another explanation that they were actually F3.3 focal reducers labelled as F6.3.  If that was true you would be able to get one to focus with a CCD camera.  I have my doubts about this story but no facts to know either way.

 

Either way, it's a defective unit.

Edited by Tom Stock, 22 October 2019 - 09:54 PM.

[asanmax]

Meade got back to me saying that it's my scope that's giving all the troubles. The baffle of the C5 is only 1" in diameter and that's why I'm getting the vignetting when using the scope, the reducer and a DSLR. I think it will work just fine with the C8 and bigger scopes especially with a CCD camera that has a smaller sensor. Time to buy a bigger scope for imaging

[bignerdguy]

I apparently also found I have one of the shorty f/6.3 focal reducers that according to my calculations is running somewhere around F/4-F/4.8 or so.  However I have been able to get it to focus on a Mead 8" OTA as long as I keep the distance between the top of the reducer body to the sensor on my DSLR at no more than 95mm.  From the T-ring to the FF/FR should be no more than 50mm, though in my case it is more like 57mm.  I get just a bit of vignetting and cutoff around the edges and corners but the center turns out pretty clear and flat.  I have been able to use both an Orion 2" Nautilus filter wheel with it as well as a 2" visual back with a 2" barrel adapter and 2" filter with it and still get focus.  However if I add anything else, it puts the focal point too far aware to be able to focus. I did measure the focus distance though not as accurately as shown in this thread and found it to be comparable to what others here have done with theirs.  I got roughly a 125mm-130mm total distance to the focus point. 

[Thrifty1]

A little more info on these "bad" Meade f/6.3 reducers that are out there.

 

I finally got around to taking 3 images with my 10" LX200r.  One with no F/R.  One with the shorter focal length f/6.3 reducer (referred to as the "bad batch").  One with the normal focal length f/6.3 reducer.  Sorry if I'm using the wrong terminology... by shorter / longer focal length I mean the one with the shorter / longer distance when focusing the sun on a piece of paper.  Maybe that is focal distance vs. focal length.

 

I attached the reducer to the rear cell of my LX200 and then the camera directly to the reducer.  With no reducer I attached the camera directly to the rear cell of the telescope.  The camera used was a Canon T3i.

 

I took 3 photos of the same object with no FR, the shorter FR, and the longer FR.  Here they are:

Using 100% for the no FR, here is how much the other 2 were magnified so the image was the same:

Shorter FR = 240% or .416 reduction from the no reducer image
Longer FR = 160% or .625 reduction from the no reducer image (what would be expected of a f/6.3 reducer)

 

So it appears the one with the shorter focal length is acting closer to a Meade f/3.3 reducer (maybe a f/4.0 reducer).

 

I did this test today as I was considering purchasing a Meade f/3.3 reducer but it looks like I have one that is pretty close to that already.

 

As expected the vignetting got worse as the focal reduction increased.  Note that I was taking this image of a transmission tower about 1000 feet away through trees.  The blurry dark spots are the branches of closer trees.  

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[AstroNikko]

Hi folks! I recently obtained an old Meade Model 2080 203mm f/10 SCT, and ordered one of these Meade f/6.3 reducer/flatteners. Not seeing a specific back focus listed in the paperwork. The Meade #63 T-Adapter has a 45mm optical length, though. With a standard T-ring, that’s another 55mm of optical length to the sensor. So, it seems the expected back focus is 100mm from the f/6.3 FR/FF to the sensor.

Am I correct in this understanding? I read through the previous posts here, but don’t think I fully understand how the standalone focal distance of the FR/FF is used to calculate back focus distance to the sensor when installed in the optical train.

[dcaponeii]

Hi folks! I recently obtained an old Meade Model 2080 203mm f/10 SCT, and ordered one of these Meade f/6.3 reducer/flatteners. Not seeing a specific back focus listed in the paperwork. The Meade #63 T-Adapter has a 45mm optical length, though. With a standard T-ring, that’s another 55mm of optical length to the sensor. So, it seems the expected back focus is 100mm from the f/6.3 FR/FF to the sensor.

Am I correct in this understanding? I read through the previous posts here, but don’t think I fully understand how the standalone focal distance of the FR/FF is used to calculate back focus distance to the sensor when installed in the optical train.

If memory serves, the correct backfocus for the Meade 0.63 reducer/corrector is 105mm. But it's a range so you're close at 100 mm.

[Lasko]

I picked up a Meade F6.3 reducer and ran into some edge and corner issues with weird star shapes.  Searching for back focus and the Meade reducer I found several opinions that it should be 85-95mm.  Mine was at 105mm with the 50mm Celestron T-adapter and 55mm camera sensor.

 

The Svbony T-adapter is 38mm so that will be next to try when there is an opportunity, maybe later this week.

[AstroNikko]

I picked up a Meade F6.3 reducer and ran into some edge and corner issues with weird star shapes.  Searching for back focus and the Meade reducer I found several opinions that it should be 85-95mm.  Mine was at 105mm with the 50mm Celestron T-adapter and 55mm camera sensor.

 

The Svbony T-adapter is 38mm so that will be next to try when there is an opportunity, maybe later this week.

Thanks for the heads up! Is this the one you're referring to: SVBONY SV167 T-Adapter-SCT

 

Saw in the specs it listed "extension tube travel" as 30mm. Which seems to be the spacing it adds to the optical path. Overall length is stated as 50mm.

 

I'm interested in seeing how it works out for you. What size sensor will you be using? My Fuji has an APS-C size sensor.

[Lasko]

Thanks for the heads up! Is this the one you're referring to: SVBONY SV167 T-Adapter-SCT

That is the exact one, and I was expecting it to be 30mm and then use a  5mm and/or 10mm extension with it.  Turns out it is 38mm effective length from the front of the T-adapter to the front of the T-ring.  Nothing on it measures 30mm so I have no idea where they got that.  12mm difference from the Celestron adapter should be enough to notice a change.  50mm must be the inside diameter of the threads on the FR end.  There isn't anything else that measures 50mm.

 

I'm using it with the D7000 APS-C.  If that works well I might try the D800 FF just to see what happens.

[AstroNikko]

Using this focal reducer calculator, I think I understand this a little better. Assuming the Meade f/6.3 reducer/flattener has a 240mm focal length, using a backfocus distance of 105mm with my Meade 203/2000mm SCT it should achieve a focal ratio of f/6.3. However, I noticed that with the NexStar 8SE at 203.3/2032mm, that same 105mm backspacing yields a focal ratio of f/6.4. Although by extending the backspacing a millimeter or two, it can achieve a focal ratio of f/6.3.

 

I'm wondering if this is significant enough to affect field curvature in the manner that you've observed.

 

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Also noticed that when using the combined 100mm backfocus distance that the Meade T-Adapter and T-ring would provide, the focal ratio of the 203/2000mm SCT would also be f/6.4 by that calculator.

 

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Found a little more info after some reading. Can calculate working focal length after plate solving (FL = Pixel size / tan( ArcSecPerPix )), measuring against a target at infinity (see post).

 

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Ok, further down in that post, it looks like Meade recommends 85mm of backfocus with the f/6.3 reducer/flattener. So 30mm of spacing in addition to the 55mm provided with a standard T-ring.

Edited by wcoastsands, 10 February 2021 - 03:30 AM.

[Lasko]

I think you're on to something with the calculator.  I also did the "try to set the door on fire with a flashlight" test with the Meade reducer and measured it at 215mm including the 2mm built-in space.

 

It was a clear enough outside for a few test frames last night and using 95mm back focus the image was improved.  The first image at 105mm had many half moon shaped stars at the edges and corners.  In the new image there are only a few half moons in the corners and close to one edge.  The recommendation for 85mm may be right on.

 

As far as the SV167 adapter, I never realized it before but that adapter is actually a 7.7mm SCT adapter and a 30mm extension tube.  Next try will be with a 20mm extension tube so total distance will be: 2mm + 7.7mm + 20mm + 55mm = 84.7

 

I still may opt with going with the Celestron adapter since I'm also concerned about using it with a UWA eyepiece.  Other than photos I was hoping to use it for wider views of Andromeda or other large fields.  It would probably work great for a small sensor camera though, even at 105mm.

[AstroNikko]

I ordered a William Optics SCT to M48x0.75 thread adapter. The total length is stated as 27mm, but I'm not sure if that also means optical length.

 

Decided to go with M48 instead of a standard M42 T-adapter because I already have a stockpile of M48 spacers, including an adjustable one, and a standard length M48 T-ring as well as a short one for the X-mount.

[AstroNikko]

The WO SCT to 2" adapter arrived. It has an optical length of 13.5mm. Total tube length with threading (minus the SCT threaded nut) is 19mm.

 

The flange focal length on the Fuji X-T100 is 17.7mm. I measured out 67.3mm worth of backfocus spacing from the base of the WO adapter tube to the flange of the T-ring for a total of 85mm from the Meade f/6.3 FR/FF to the sensor. Will try to test this tonight.

 

[AstroNikko]

Had a chance to get out and test tonight. I'm a bit underwhelmed by the results:

• 87.2mm working distance (0.634arcsec/px, 1269.04mm effective fl, f/6.2)
• 104.2mm working distance (0.679arcsec/px, 1184.93mm effective fl, f/5.8)

Using the focal reducer calculator, the focal length of the Meade f/6.3 FR/FF appears to be 215.8mm.
 
Based on these results, I think the working distance should be 91.5mm (0.629arcsec/px, 1280.0mm effective fl, f/6.3):

 

91.5mm = (2mm FR/FF) + (13.5mm WO SCT-M48 adapter) + (47.3mm spacing) + (11mm X-mount adapter) + (17.7mm Fuji X-T100 FFL)

 
Will test this again next chance I get. At 0.629arcsec/px, I'm expecting slight oversampling. However, I'm hoping to see improvements to field curvature and coma.
 
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Edit: I kicked the numbers here. Corrected the plate solved values.
 
Also realized I don't fully understand how the Focal Reducer calculator works. I don't think the resulting values are correct.
 
The problem I'm working on now is how to calculate the working distance given the following:

• Pixel size = 3.9 micron
• SCT diameter = 203.2 mm
• SCT focal length = 2000 mm
• Effective focal ratio = f/6.3
• Effective focal length = 1280.16 mm
• Effective image scale = 0.628 arcsec/px

When the applied working distance of:

• 87.2mm yields an image scale of 0.634 arcsec/px
• 104.2mm yields an image scale of 0.679 arcsec/px

I haven't worked out the rest of the math yet.

Edited by wcoastsands, 22 February 2021 - 04:32 PM.

[Lasko]

I managed a few test frames last night despite the full moon.  It did a fine job on the moon though, which is my profile pic now.  

 

With shorter back focus it is better but still would need cropped on the edges/corners.  The ASI did better because of the smaller sensor.  I suppose I could keep going shorter until the bad part is forced off the frame.  Kind of defeats the purpose though.

 

Here is a single 10s frame of M42 with the D7000 APS-C and 85mm back focus:

 

 

And here is a single 10s frame from the ASI294MC and 100mm back focus:

 

[michael8554]

I believe that because the Focal Length varies with the primary mirror position at focus, which will depend on how long your image train attached to the rear is, trying to find the spacing to achieve a 1280mm focal length isn't necessarily going to result in the best images.

 

Just adjust for best star shape with your setup.

[Lasko]

Just adjust for best star shape with your setup.

That is really the answer there, and I finally had some success getting an edge-to-edge usable image so thought an update was in order.

 

The ASI image I posted last works out to 0.61x @ 100mm and has edge and corner problems.  On Thursday I tried again at 90, 80 and 70mm to find what worked.  It was better each time and at 70mm the entire frame was in focus.  This worked out to 0.68x which I'm perfectly happy with.  Next will be to test out the APS-C to see if 70mm will work.

[Feccy]

I believe that because the Focal Length varies with the primary mirror position at focus, which will depend on how long your image train attached to the rear is, trying to find the spacing to achieve a 1280mm focal length isn't necessarily going to result in the best images.

 

Just adjust for best star shape with your setup.

Thank you for pulling me out of this rabbit hole - I have been in it for days!!

 

I'm new to AP but have had my scope 20 years - I'm currently trying to find the optimum back focus with a C8 and an Antares f6.3 FR (220mm FL). I already had the Celestron T-adaptor so with that and a Canon 550D I have an effective FL of 1255mm (from plate solve results & Astronomy Tools 'CCD Resolution Calculator') with a 103mm back focus (sensor to outer flange of adaptor) length. I am getting quite a bit of coma so am awaiting a clear sky to try a reduced spacing of either 95mm or 98mm - I've given up on calculating this due to the variables of scope focal length with mirror move & exact measurements between the various items on the imaging train (measure to the edge of the FR or the face of the lens on the FR or the centre of the lens on FR - I've stopped trying/caring tbh!)

 

All that matters is a sharp image and as I'm still a noob with focusing (just got a Bahtinov Mask last week) there's probably room for improvement there too

 

With the various adaptors I have the next step, should 95/98 not work, is 85mm which may be too much but I'll try if it improves things.

 

Image below from my 2nd only outing with my new mount (so be kind) which shows the coma around the edges (there's damage on my camera sensor causing the blotches in the centre which is in progress fix wise) that I am trying to fix. I'm not sure my focus was 100% and am open to advice if this is not a coma issue?

 

 

Great thread btw everybody!!

[MarMax]

Even though this is an older thread it's a great read and very informative for those wanting to mess with f/6.3 reducers. I'm not doing AP really, just a little afocal smartphone imaging, but mostly visual. I like the extra field that the f/6.3 provides in the C11.

 

The other thing, for those that like to use an f/6.3 for visual, the older Celestron #93519 2" diagonal has SCT threads in the body which makes it very adaptable. You can remove the inlet connector and then thread the diagonal onto the f/6.3 that's mounted on the scope visual back. The only precaution is to use a short spacer (like 1mm) to make sure the f/6.3 does not make contact with the mirror.

 

With the #93519 diagonal connected directly to the f/6.3 reducer the light path through the diagonal is 70mm which leaves 105 - 70 = 35mm from the body of the diagonal to the field lens of an eyepiece for optimum backfocus. It's very easy to work with this 35mm distance +- a bit of course.

 

Here is a picture of this setup with an ES 18mm 82 eyepiece and NexYZ cell phone adapter. And there is a 1mm spacer between the f/6.3 and the diagonal that you can't see in the picture.

 

 

 

And a Moon picture with the above setup in the C11. More to present the FOV than image quality since half the Moon is not in focus.

 

Edited by MarMax, 25 March 2021 - 10:55 PM.

[Feccy]

Stumbled across a discussion on another thread that suggested using 'CCD Inspector' would help - there's a 30 day trial - 3D plot result below from a RAW light image which suggests there is a problem - as soon as the UK cloud disappears!! I'll adjust back focus & see if there's an improvement - interesting stuff

 

[Sky King]

So with the moon and all the light pollution last night, I decided to try my Meade too short FR out on my C8.

 

I started with a 95mm back spacing from FR to camera. Using the method given by Rickster in post #4 I got a F-Ratio of 4.51, 915mm effective focal length, pixel scale of .845. 

 

So then I took a 20mm spacer out of the chain and at 75mm back spacing got an F-ratio of 5.42, 1100 effective focal length, and pixel scale of .701.

 

The size was 15x11 at 75mm back space and 18x13 at 95mm back space. So at the lower focal length the view was wider.

 

But I expected these overall results to be reversed: At 75mm I thought the F-ratio would be lower not higher. I like the stars better at 95mm, less bloating. 

[wylieoncoyoterd]

Sort of ran into this thread by accident 

I purchased a Meade 10" SC f6.3 scope back in the 90's. I was, a few years later, imaging with a SBIG 2000XCM camera and purchased the Celestron f6.3 reducer corrector for use with it. I later purchased a SBIG 4000XCM camera, and the Meade f6.3 reducer/corrector set, that came with a boxed extension ring set of various lengths, that you can use to change the focal ratio and width of field of view. I don't see this ring set being mentioned herein this conversation. Maybe I've missed that?

I still have the scope, although it is currently loaned out along with the 4000XCM camera to a good friend, a professional radio astronomer employee at the Owens Valley RO, Big Pine, CA for use with local school student star parties. I personally prefer the 10" f6.3 model to the 10" f10 Meade's; the much brighter viewing and faster imaging of the f6.3 model is worth the larger secondary obstruction IMO.