New Focal Reducer

[centroid]

Have I found what I've been looking for?

That is a x0.5 Focal Reducer to use with my 12" LX200R and SXVF-H9C.

Following on from an earlier 'thread' of mine on this subject, I came across this today:

http://www.telescopehouse.com/acatalog/info_52066.html

My quest was/is as follows:

While I can use my Celestton x6.3 FR with SXVF-H9C camera, I can't use my x3.3 (its only suitable for smaller format CCDs).

I want be able to get down below x6.3, and a x0.5 seems to be good compromise between the x6.3 and x3.3.

One option was the Atik x0.5, but this really is a budget optic, and reports from forum members were less than complimentary.

Next was the Rini x0.5, but there were mixed opinions on this, and in any case its no longer available.

So, is this apparent newcomer, the answer to my quest. Orion optics have a good name, and at 75 quid, its neither budget, nor expensive.

As its 'new' then I guess its unlikely that anyone on the forum has used one, but you never know

Dave

[Psychobilly]

HI Dave, have you tried using the spacers that came with the meade f3.3 to give you different reduction ratios an tried that with the SVX to see what effects they have on field flatness and vignetting?

Billy...

[centroid]

Hi Billy

Each focal reducers requires a specific spacing between it, and the CCD, in order to achieve the stated focal ratio.

For example, the x.63 require something like 105mm of spacing. Given manufacturing tolerances, some variation the theoretical figure will always be present, and with the x.63, I use 100mm to achieve the x.63 figure.

Unfortunately, the x.33 was designed in the days when small format CCDs were the norm, and with my old MX7c, it worked fine.

While I could move the CCD closer to the x.33 FR by removing the spacers, which would effectively increase the focal ratio, the FR would then be operating outside of it's optimum range, and the distortion and vignetting would likely still be there, when used with the SXVF-H9C.

Anyway, thanks for input.

Dave

[Psychobilly]

AFIK the whole point of the variable kit that comes with the Meade f3.3 is to enable you to operate it at various ratios... but i suppose they were only using a small central part of the reducer and could get away with it. I agree it's pants with anything other than DSI sized sensors...

Sorry I don't know what the Orion's going to be like - I have one 1.25" 0.5x reducer but don't use it any more bought it for use with the old ETX but use to struggle to get focus with it...

A few experiments and analysis with ccdinspector might throw something up...

Billy...

[Merlin66]

Been there, done that!

On my 12" LX200 I ended up using the Optec NextGen 0.5 reducer, with the correct CNC spacers for the Canon350D it gives excellent results!

Now that I've gone over to the "dark side" and concentrate on spectroscope work, it doesn't get used all the time, but it's there when needed.

2000% better than either of the Meade reducers ( I have both)

Worth checking out.

Billy.... the various SCT to T2 adaptors for the 0.33 were supplied not for modifying the ratio as much as for maintaining a design distance with different small CCD camera body sizes, as per the Instruction sheet ( copies available on MAPUG site)

[Psychobilly]

Thanks for clearing that up Merlin...

Where have I read that it can produce ratios from f3 and f5 then .... :scratch:

http://www.opticsplanet.net/meade-ccd-f3-focal-reducer.html

http://www.telescopes.com/telescope-accessories/photographic/meadef33ccdfocalreducerfieldflattener.cfm

Seeing as everyone using the same text it may have come from Meade perhaps :withstupid:

Billy...

[bern]

Dave, I reckon the Orion unit will most likely be the same or next to the same as all the other brands out there.

After all there's only so much you can do with a simple two element design of around 85mm focal length.

£75 is taking the pee imho!

bern

[Merlin66]

Couldn't find a copy of the original instructions on the Meade site ( or the Californiastars.net, where I got my "back -up" copy), but to be completely open, yes the instructions do say that with the Meade Pictor CCD imager with the 15mm Spacer on an f10 system, it should give f5.

The 30mm spacer is quoted as f3.3 and the 1.25" adaptor f3.0

"Other brands of CCD camera may vary slightly from the focal ratios in the above table"

http://www.mapug-astronomy.net/ragreiner/opticlens.html#Top

This reference gives info on back focus spacing etc.

Sorry for the confusion!!

[centroid]

Fair comment Bern, and probably right.

In which case then 75 quid for something that's no better the 30 quid Atik, is indeed taking the 'P'.

The Optec sounds interesting Merlin, and I'll make enquiries as to availability and cost. Thanks for the info on that.

Billy, as Merlin says, the Meade spacers qare only to allow a degree of adjustment when using different cameras, where the CCD is likely to be set a various distances from the camera/FR interface.

Apart from these, I have a set of 'T' thread spacers, from 6mm upwards, which enables all the distance combinations I require.

Reducing the spacing from that required to achieve x.33, would comfortably increase it to x.5, but the H9C CCD would still not be fully and correctly illuminated.

Dave

P.S "quid" = no pound sign on this Aussie keyboard.

[centroid]

There you go, here it is:

http://www.optcorp.com/product.aspx?pid=3531

Looks interesting.

Dave

[iancandler]

Have you tried using the variable T adaptor that comes with the 3.3 on the 6.3 as my understanding is that the amount of reduction depends on the focal reducers distance from the chip.

Given that your camera has T threads to attach the nose piece you should be able to connect the variable T adaptor rings direct to the camera, then experiment with spacing to give the desired result.

[Psychobilly]

I played with that before ... some terrestrial test shots here...

http://picasaweb.google.co.uk/PsychoBillyUK/8SCTFocalReducerTests#

Billy...

[MartinB]

The 3.3 is supposed to be a field flattener like the 6.3 and this is why the spacing might be an issue. In reality I suspect that it isn't actually much of a flattener and that there is a lot of latitude when it comes to spacing.

Roland Christen did a report on the LX200R which, because it gives a flat field, shouldn't be compatible with a 6.3 reducer. Roland's observation was that the reducer should work alright with this scope and doesn't do much flattening. I would like to bet that the 3.3 is the same.

Anyway, the proof of the pudding and all that. I will be very interested to hear how you get on with it Dave.

If that is the case then Billy is spot on and reducing the spacing should enable x0.5 to be achieved. Because of it's wider aperture the 3.3 is likely to produce much less vignetting than any 0.5 reducer. The vignetting is down to simple physics, not the quality of the optical construction.

That said Dave, I calculated that a 1.25 reducer at 0.5 should cover the 285 chip with just about acceptable vignetting..

The other problem will be the lack of field flatness of the SCT design. You are effectively taking a very wide field and compressing it onto a small chip. Those stars at the edge of the field are likely to be pretty elongated

[jcm]

I was looking into getting a 0.5X reducer for my C9.25.

After lots of searching it came down to the Optec Next Gen 0.5 reducer. These are supposed to have a 17.5mm flat field area with would cover my Atik 16HR . As I still could not make my mind up I got a Starlight Feather Touch 10:1 focuser instead

John

[centroid]

The Celestron x.63 does work fine with the LX200R, and and images taken with it via the H9C, show 'tight' round stars right out to the edge/corners.

With the Meade x.33 stars at the edge/corners are very distorted, when using the H9C. When I used the MX7C, the problem didn't occur, due to it's much smaller 'chip' size.

So, to my thinking, its a matter of the x.33 not illuminating the H9C's CCD, with a flat field. As I said earlier, the x.33 has been around for may years, and back to a time when small CCDs were the 'norm'.

I'm pretty certain, that when I first got the H9C, I played around with the spacing, but could not get a 'flat field' onto the H9C's CCD, and put the x.33 back in it's box, where it has remained since. This was the reason I bought the x.63 at the time.

Merlin's comments, and the Spec of the Optec unit, would seem to indicate that this particular focal reducer, would do the job nicely.

Its just a pity that currently the pound is performing very poorly against the US Dollar

Dave

[centroid]

Just found this review comment on the Optec Focal Reducer.

NextGen .5x Telecompressor

I've used it with an SBIG ST2000XM and have seen a lot of vignetting around the edges.

Hmmmm??

Dave

[MartinB]

Sorry Dave, I was forgetting your scope is the 200R.

This is well worth a read Dave, it is discussing the Astro Physics reducers and is written by Roland Christen. However, much of the article is generic and is a great guide to working out an appropriate focal reducer.

http://www.astro-physics.com/tech_support/accessories/photo/Telecompresssor-techdata.pdf

[centroid]

Thanks for the 'link' Martin, I'll have a read when I get home, as we will be heading for airport soon, and the 'long haul'.

Something like 26+ hours, door to door

Dave

[darditti]

For what it is worth, I experimented with a 0.5 (ish) times reducer in 1.25" format (the Atik that Bern sells) with a 285 chip and SCTs. Basically the result is bad vignetting. So you can only use a part of your image, in which case, why pay for that chip? I went back to using the Meade 0.63 reducer, which seems to be the best budget solution for this chip size, though you do get distorted stars at the corners of the field with this. All this is going to be almost independent of scope type, and I don't expect it will be different with a different make of reducer of roughly the same type, as Bern says.

Focal reducers overall are a hang-over from the early days of CCD technology, with tiny chips. They are becoming less and less useful as larger chips become the norm, and I expect them to soon disappear. As you go to larger chips you are getting more or less everything common telescope designs will give you, in terms of a properly-illuminated field without aberrations. The 285 type is still small enough to benefit from a bit of reduction, but not more than x0.63. I suspect even a larger format 0.5 reducer (which would not give so much vignetting) would not give a good result with a 285, but I am not certain as this accessory doesn't seem to exist.

David

[centroid]

Thanks for your Input David.

As I said to Martin, with the x.63 on the LX200R, the stars are 'clean', right out to the corners, but this is more to do with the "R" (now ACF ) optics of the scope.

The Optec x.05 unit is spec'd for a CCD with a diagonal size of 17.5mm (ICX 285 = 11mm diagonal), and use with an SCT, but of course the 'proof of the pudding, is in the eating". Unfortunatley, it would cost $245 to taste the particular pudding.

Merlin, comments that he uses the Optec FR, and finds that it works well for him, but I don't know if that's with a 285 sized CCD.

Dave

[bazza]

Dave,

First of all, welcome home. Although, I expect you have mixed feelings, leaving your close family in Oz.

The time you have been in Oz has certainly gone quickly, so I hope it's not long before you're all reunited again.

With regards to this thread, I've just taken receipt of an Astro Physics .67 reducer (they call it a telecompressor). Although designed at .67, this is at a distance of 101mm (4") ideally. Well, I'm going to fit the .67 in my Moonlite focuser and this will create a distance between chip and reducer of approx 5" (124mm) - this is going to increase the speed to about f5.8 but well within the 11mm given for the SXV- H9/9C chip. (Again, as per the article by Christen).

I'm just waiting for an adaptor to be completed by someone locally, then I will fit it.

I'll let you know how it fares.

(The AP reducer is ideally suited to the LX200R). see Ian King's website for confirmation of that!

Kindest regards and again, welcome home,

Barry.

[centroid]

"NextGen .5x Telecompressor

I've used it with an SBIG ST2000XM and have seen a lot of vignetting around the edges."

SBIG ST2000XM uses Kodak KAI-2020 CCD: image size digaonal = 14.8mm

SXVF-H9C uses Sony ICX 285: image size diagonal = 11mm

Optec claim flat illumination of CCD up to 17.5mm diagonal.

According to the guy, who posted the 'above' comment, he found a lot of vignetting with the ST2000M[/]

So, who do you believe :?

With the 11mm diagonal ICX 285 be ok, :scratch: .

Anybodys guess I suppose :?

Dave

[centroid]

Hi Barry

I'll be very interested to here how it works out with the AP telecompressor.

I suppose I could try extending the distance with the Celestron 6.3, but of course theoretically, this will then be at a point beyond the light cone convergence, I think :scratch: .

Dave

[centroid]

Just calculated that at 120mm spacing, the 6.3 would theoretically be 5.79 (6.34 at 105mm)

Dave

[centroid]

140mm to theoretically achieve f/5, but I really don't think this would work.

Dave