200x with small apo refractors ?

[Dinosour23]

Hey there ! I was wondering what is your personal experience using short tubed 80-100mm Apo refractors (450-650mm) for planetary viewing.

Right, it's not the right tool for the job I realize that, but still, what did you manage with them ?

Is 250x on a good night... Is that a waste of time to even try ?

Reason I am asking is, i am thinking about buying an eyepiece at 4mm that will allow me to go up to 200-220 from the x180 I currently use often.

Thanks for any replies!

[John]

I have a Vixen 102mm F/6.5 ED refractor which I have used for planetary viewing reasonably often. The viewing conditions are the most significant factor but if they are good then the scope will work well at 180x - 200x. Jupiter usually shows the crispest details at a bit less than this (which is usual with any scope) so 130x - 150x is best for that target. On the Moon and double stars I can exceed 200x although I don't tend to use more than 221x simply because my shortest focal length eyepiece is 3mm. I doubt that I would go as far as 250x. My ED120 refractor can handle that and a bit more though. Having owned 80mm and 90mm ED refractors I think you would need to reduce the magnifications to suit the smaller apertures unless you are using something superlative like a Takahashi.

It's worth remembering that the best magnfication is the one that shows the sharpest and most contrasty images rather than the highest you can pile on. Often "less is a bit more" when observing the planets

[kenny k]

Depends on your sky and conditions,i never go beyond my 10mm delos on Jupiter as my 6mm is to much 99% of the the time with my equinox 80.

Kenny

[Stu]

I would tend to agree with John's comments on this. I find for planetary viewing an exit pupil of 0.5mm is a reasonable minimum which gives x160 in an 80mm and x200 in a 100mm.

As said, seeing conditions play a big part in the results on planets, but personally I do enjoy viewing through apo's of this size.

Floaters in your eyes can be an issue though at exit pupils of this size.

[Piero]

I also agree with previous comments. Safe territory up to 0.6-0.5mm exit pupil for small refractors. You can push a bit more with the moon. 

Although the object becomes larger, the resolution is the same, and since you are looking for details, it is better not to magnify too much and get a more defined image. 

[chiltonstar]

With my ED80, x160 is about as good as it gets with planets - the contrast and detail are maintained and it's ok for eye relief comfort. I do use higher mags with it, but only for double stars where contrast is usually less important.

Chris

[Dinosour23]

Thanks John, Kenny, Mr Sumurian and Chris !  Exactly what I wanted to know

It seems like a specialized purchase to target 220-240x is hard to justify for a 90MM refractor !

Once again SGL saves the public some CASH ! 

[ronin]

What is the 90mm scope, at that size sounds as if it might be the WO Megrez 90, not that many 90mm scopes around, but 4mm would not deliver the magnification you give. Whether something like the ES 102 Triplet with a 4mm or 3.5mm would deliver is boarderline.

The next question is which eyepiece?

A 4mm plossl is very doubtful, whereas a 3.5mm TV might even if more magnification.

I would expect my 80mm apo triplet to match the 90mm Megrez as the Megrez is still a doublet.

Whether the 3.2mm BST will work in the Megrez I do not know, never tried it. Bought that eyepiece for another reason.

You also are in the region where a single eypiece may not make it but say a TV powermate and an eyepiece might.

So not easy to supply a simple answer.

The other aspect is that you get a 5mm and if that works you look at a 4mm, if that works then a 3.5 or 3.2. Eventually you stop buying when one does not work. So the last purchase is a loss. Unless you can borrow/try a selection first.

[Stu]

What is the 90mm scope, at that size sounds as if it might be the WO Megrez 90, not that many 90mm scopes around, but 4mm would not deliver the magnification you give. Whether something like the ES 102 Triplet with a 4mm or 3.5mm would deliver is boarderline.

The next question is which eyepiece?

A 4mm plossl is very doubtful, whereas a 3.5mm TV might even if more magnification.

I would expect my 80mm apo triplet to match the 90mm Megrez as the Megrez is still a doublet.

Whether the 3.2mm BST will work in the Megrez I do not know, never tried it. Bought that eyepiece for another reason.

You also are in the region where a single eypiece may not make it but say a TV powermate and an eyepiece might.

So not easy to supply a simple answer.

The other aspect is that you get a 5mm and if that works you look at a 4mm, if that works then a 3.5 or 3.2. Eventually you stop buying when one does not work. So the last purchase is a loss. Unless you can borrow/try a selection first.

I think we've established that the 90mm scope will not deliver the x240 or so views the OP was looking for. Regardless of eyepiece it would give an exit pupil of 0.375mm and be very dim and prone to floaters. Possibly ok for lunar and doubles but not planetary.

[YKSE]

I think we've established that the 90mm scope will not deliver the x240 or so views the OP was looking for. Regardless of eyepiece it would give an exit pupil of 0.375mm and be very dim and prone to floaters. Possibly ok for lunar and doubles but not planetary.

 Stu, Clear and concise summary

[mikeDnight]

I use a Takahashi FC 100D which performs wonderfully at high magnifications. Currently I'm limited to X296 which is great for the moon when the seeing is steady. Technically the limit of the scope is X200, so that any magnification above this is simply enlarging the image and not really showing you more detail. The fact that the Tak takes magnification well is an indicator of its fine optics.

For the best lunar and planetary views I generally use a binoviewer and a power of around X200.

Mike

[michael.h.f.wilkinson]

I tend to push my 80mm F/6 no further than about 120-144x. I am sure it could handle 160x, but I do not feel even 144x adds more detail than 120. On the moon it does take a bit more. For this reason my C8 is really my main planetary scope.

[Jon_Doh]

I  have a Skywatcher 120 APO and viewed Jupiter at 300x a couple of nights ago with fairly good seeing conditions.  An APO can handle higher magnification, but will be limited by seeing conditions.

[jetstream]

My 90mmAPO triplet will go 150x on the planets under VG conditions, my SW120ED will take 240x under similar conditions. When conditions are this good though, the VX10 comes out and neither will compete with it on the moon, planets or DSO. Splitting stars and star color is a different story. This 120mm doublet bests the 90mm APO on the stars for color and resolution splitting doubles.

Same thing for solar, under VG conditions the SW120ED bests the 90mm soundly.

[Stu]

I use a Takahashi FC 100D which performs wonderfully at high magnifications. Currently I'm limited to X296 which is great for the moon when the seeing is steady. Technically the limit of the scope is X200, so that any magnification above this is simply enlarging the image and not really showing you more detail. The fact that the Tak takes magnification well is an indicator of its fine optics.

For the best lunar and planetary views I generally use a binoviewer and a power of around X200.

Mike

Mike, do you not find floaters an issue at such small exit pupils?

[mikeDnight]

Hi Stu.

I find floaters can be a problem especially if I'm using a single eyepiece. For most of the time on the moon and planets I use a binoviewer, which seems to reduce the problem of floaters. I also feel that it helps me to see better when the atmosphere is turbulent. It seems the floater and turbulence problems in a single eyepiece are cut down by half when I use a binoviewer.

Mike :-)

[Dinosour23]

Yes guys it is indeed a Megrez 90FD ! 

OK, so I understand what you are saying about a bigger picture with no more detail. I have seen that before, ugly large image -very soft and artificial... That is not what I want ! 

I thought about still getting the Meade 4.7mm, but put the 1.3x barlow element under it (Baader Q barlow).

Sounds more like a plan ?

I currently have a Luminos 7mm that could accept the full x2.25 in good nights, and I'll use the Meade as stock/1.3x at most.

[Stu]

Interesting review here.

http://www.cloudynights.com/page/articles/cat/user-reviews/megrez-90-fd-fluorite-doublet-review-r2769

A lot will depend upon your skies. More stable US seeing will help to give better results at high mag, but it seems a capable scope.

[John]

I had a Megrez 90 for a while. It seemed a nice scope. 180x was about it's "sweet spot" high power. 220x for the Moon and double stars under good observing conditions.

[mikeDnight]

I had a Megrez 90 for a while. It seemed a nice scope. 180x was about it's "sweet spot" high power. 220x for the Moon and double stars under good observing conditions.

I seem to remember reading that E. E. Barnard felt that X180 was his preferred magnifying power for the planets while using his 5" F15 refractor.

I've certainly found myself lingering around this power over the years, no matter what the aperture of the scope. Probably, if I were only allowed one planetary eyepiece, it would be one that gave me X180. I've found the image to be plenty big enough to reveal significant detail, while at the same time being capable of holding a sharp contrasty view.

Mike.

[Moonshane]

Unless you need long eye relief a 6-3mm Nagler zoom would be an option

[Dinosour23]

Thanks ! More power to the x180 max ... Seems like wanting more out of these is greedy ! But It sure is enough.

I actually looked through a Nag Zoom but I was put off by the fov ? I use a manual Alt Az with degree circles and often spot&call someone to also take a look so it is better for me and the other observers to have more field to work with !

The view was really really crisp though... But, I convinced myself it was seeing conditions ;)

[Stu]

You 'need' a Televue 3.7mm Ethos SX then! Would 'only' give x150 but with a 0.59 exit pupil would be great, and still a 0.73 degree field!!

Bit pricey though ;-)

[Dinosour23]

Yea, but I heard that once you buy one Ethos you begin a set craving frenzy so I am being very very careful ! 

Plus I really wanted to get a Quark so need to put money aside for that first  

Any special objections to the Meade UWA 4.7 + 1.3 Glass permanently screwed ? 

[Stu]

Yea, but I heard that once you buy one Ethos you begin a set craving frenzy so I am being very very careful !

Plus I really wanted to get a Quark so need to put money aside for that first

Any special objections to the Meade UWA 4.7 + 1.3 Glass permanently screwed ?

I don't know much about Meade eyepieces so won't comment.

A used 3 or 4mm Radian or 3.5mm Nagler might be nice?