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F15Rules

Help with eyepiece/barlow combinations please?

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Talking to Peter Drew a number of years ago regarding Binoviewers and Barlow lenses, Peter said its nearer 4X amplification. He's been in the telescope manufacturing game a long time, so I'm inclined to trust his judgment on optics. I rarely screw a barlow directly into my binoviewer; instead i tend to use a shorty celestron ultima sv 2X barlow, which increases the distance between the barlow lens and the field lens of the eyepiece and so would increase magnification slightly over the screw in method. I have on many occasions screwed a SW delux barlow into my binoviewer and then fit the bv to yet another barlow with good results. 

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23 hours ago, Alan White said:

@mikeDnight as always your reports / recollections have me hooked.
I am between yourself. @F15Rules and others moving towards a binoviewer with my very fine ED103s Vixen.

One question on the pseudo Masuyama's, were any made with rubber eye guards at all?
It is something that I 'need' to be present on an eyepiece.

Pm sent re eye guards.

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Well, I did get out last night from about 9.15pm til 10.30pm.

I used a combination of cyclops and binoviewing, and was just delighted with the quality of the seeing here last night. It was a little misty, no wind whatsoever, and a few degrees above freezing.

The 85% illuminated moon was my sole target apart from one very quick look at M42 in Orion - the nebula was all but invisible due to the brightness of the moon, and of course no sign of E and F stars, but the Trapezium main four were pin sharp and really nicely defined.

On the Moon..first off was the Carton 7-21mm zoom. The 7mm setting gave a nice 60 degree field at 148x. I could immediately see, 100%, the "A" craterlet in Plato. And, unlike a few nights ago, when I saw it as a tiny, light coloured smudge, this time it was a sharply defined tiny circular pit.

I felt I might be able to see more as my night vision improved, so I put in an 18mm Tak mc@ ortho of known excellence, with the Baader 2.25x zoom, giving 130x. This time I had a very distinct impression of intermittently seeing other objects, and the overall vista was jaw droppingly sharp: this is where I felt my Tak EM2 equatorial mount came into its own - it has a simple, single axis RA drive, but it just holds the object right there in the centre of the field for half an hour or more with just a simple visual polar alignment. I slotted in the Carton 10.5mm 65degree SWA -this is the ep that I kept at the expense of my trusty Pentax XL10.5- and I put in the baader barlow, giving me  223x. This did the trick and I definitely saw 3 craterlets, all defined, tiny pits.

I decide it was time to try the binoviewer now. I only have two pairs of fairly cheap plossls for binoviewing, one at 30mm and one pair at 15mm. The latter, used without a Barlow, just come to focus with about 3mm to spare (I managed this by using several baader components all using up a bit less precious in-focus than most adapters).

The 15 mm pair only give 69x with no Barlow, but to my astonishment I got the best view of the evening! At just 69x I could glimpse 3 perfect, sharp tiny dot craterlets! I also suspected at least two other features right at edge of my vision..and the view was so much more comfortable than just using one eye: I was able to just sit there, fascinated, taking in the view for a good 10 minutes.

The whole outline of the massive crater was almost etched, with virtually no shimmering at all from the atmosphere.

It was now that I did something really stupid..I wanted to try the barlow 1.6x nosepiece, thinking that, based on other comments in this thread, I would get about 3x the native ep power, in this case that would have been 3x69, ie 207x. I was so excited to see how that view would look, having seen what I had seen at just 69x, so I put in the nosepiece and.... nothing! Just a vague blur. Try as I might I could not get focus...

By now I was quite cold, but still elated, so I called it a night and determined to figure it out inside in front of the log burner!

Of course, what I had done was screw in the nosepiece in the wrong place! Instead of screwing it into the binoviewer nosepiece, and then putting that into the Baader prism diagonal, I had stupidly screwed it into the prism diagonal nosepiece, adding the whole light path of the diagonal into the mix! So, of course, I wouldn't have got focus without a very sizeable extension tube in the optical chain - and goodness know what magnification factor that would have been?

Of course, the above is rather embarrassing, but I offer it a) so you can have a laugh at my expense, b) as a salutary warning against getting over excited and rushing things, and c) for those of you who are debating whether to take the plunge and try binoviewing, I would encourage you to try it for yourself!

I don't know how a cheap pair of unbranded plossls can deliver such a wonderful view, ahead of a cyclops view from a really good quality eyepiece, but I know what I saw, and I can verify what MikeDnight has said for a while..2 cheap eyepieces can be better than one! It must just be something to do with how the brain processes two images? Whatever it is, I'm delighted with what I saw last night 👍😎!

Thanks for reading.

Dave

 

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@F15Rules Look for a used Meade 140 APO Series 4000 2x triplet Barlow.  That's the nosepiece I've been using to reach focus since the included Arcturus 1.85x and 3.0x nose pieces are complete garbage.  They produced really odd coma-like distortions in all scopes and with all eyepiece pairs.  With the Meade, there is no indication anything extra is in the light path other than increased magnification of 3.0x.  Slowing down my scopes to around f/18 also allows the 23mm aspheric 62° eyepieces to really shine as well-corrected 7.7mm eyepieces.  I've picked up multiple copies of this Barlow for various uses for around $35 to $40 apiece.  You could compare it to your Baader and WO nose pieces to see which works best for you.

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Thanks Louis.

I've actually owned a couple of that very Barlow in the past. I liked it, but used it only for Cyclops viewing at the time as a full Barlow and didn't try it just as a nosepiece only.

They do come up for sale over here quite cheaply, so I may keep my eye open for one.

Dave

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Thanks Dave for the

a, laugh

b, warning

c, encouragement to binoview, you know I am tempted.

Also good to see you finding what Mike knows and has told us many times is spot on.

Edited by Alan White
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16 hours ago, F15Rules said:

It was now that I did something really stupid..

Of course, the above is rather embarrassing..

 

Are we related? :laugh2:

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7 minutes ago, mikeDnight said:

Are we related? :laugh2:

Yes, we are all Astronomers and doing something silly is our 'family' trait 😉

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On 04/02/2020 at 12:24, mikeDnight said:

You could measure the exit pupil to find the magnification, but the measurement needs to be precise.

Exit pupil = D/M therefore M= D×E

I think! 

Easier to put a star in the centre of the FoV and time how long it takes to drift to the edge. Do it a few times in mono view and a few times inserted into the binoviewer/barlow and then divide one average by the other to get the multiplication factor. So long as there is no vignetting of course. :)

 

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17 hours ago, Ricochet said:

Easier to put a star in the centre of the FoV and time how long it takes to drift to the edge. Do it a few times in mono view and a few times inserted into the binoviewer/barlow and then divide one average by the other to get the multiplication factor. So long as there is no vignetting of course. :)

 

I figured out mine by setting up my telescope indoors in the daytime with a yardstick at the other end of the house.  I then imaged the width of the ruler shown in the eyepiece with my cellphone camera for each barlow/binoviewer combination and did the math to get the relative magnification factors after downloading the images and viewing them at full resolution.  The key thing to make this work is to ensure that the field stop is clearly imaged, so keeping the phone parallel to the eye lens and at the eye relief distance is imperative.  You can also do it simply by eyeballing it without a camera if you don't mind a couple of percent error.  If there is significant vignetting, you have to make a judgement call about where exactly the field stop appears to be.  If the edge fades completely to black, crop the center from both images by the same number of pixels and check the amount of ruler shown.  For this to work, the exact same part of the central image has to be used to avoid eyepiece distortion coming into the calculation.

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