Borg 55FL f/4.5

[GlenM]

Does anyone use this scope for casual grab&go but mainly for imaging? Any help would be appreciated. Looking at using it with my Olympus OMD EM10 II.

 

Thanks guys,

Glen.

 

 

[nicoscy]

I use it as a finder with a TS 2" flattener. You'd get horrendous field curvature without a flattener...

[GlenM]

Thank you. I thought that might be the case.

 

Glen.

 

 

[nicoscy]

Glen,

With the 2" TS flattener on the diagonal, I get 6.2° of true field of view which is flat. It happens the distance is more or less spot on for visual. Without it, I had to refocus to see either the stars at the edges or in the center - I had to pick what would be in focus. It is a very fast scope with short focal length, so field curvature due to the short focal length cannot be avoided.

However, depending on camera to be used and if you are in the mood to experiment with spacing, you should really get a more or less flat field for imaging as well, or buy the imaging configuration that Ted of Hutech Borg sells, as well as the visual adapter.

EDIT: FLO has the Borg stuff as well - so best bet is there. I am sure they can also advise on camera adapter for your Olympus.

You could get a pre-owned fixed FL lens and use that, plus something (like the new SW 72mm ED) for quick visual. I recently bought for EAA, a Canon 300mm L UMC f4 lens - let's call it a 75mm f4 flat field refractor, plus the Geoptic adapter to mate it to my ASI 183. Plenty of good lenses on eBay plus adapters to whatever camera.

[GlenM]

Thank for the information. I am at the moment going to use my Olympus 40-150 Pro zoom. It's just that it can be a little difficult to attain exact focus. Obviously I can't use it as a a grab&go but it is a superb lens for terrestrial imaging. Just bought a Hoya Red Intensifier RA54 filter to use with the lens. Also going to try the SharpStar II mask.

 

Glen.

 

 

[nicoscy]

Glen,

Another option is the Vixen 55FL. Seems like a fine little scope and had it been available when I wanted such a scope, I would have bought this one instead of the Borg...

[GlenM]

Thank you. The Vixen looks very interesting.

 

Glen.

 

[GlenM]

Just done a search on this and couldn't find out if it is Fluorite crystal or Fluorite glass (FPL53). I would have thought if it was crystal they would have shouted this out in their specs.

 

Glen.

 

[nicoscy]

Direct from Vixen. This: 蛍石 means fluorite in Japanese. Google translate says flourite and both APM and TS state fluorite and not FPL53. If it was FPL53, it would have been probably near half the price.

But again, short focal ratio. You still need to mate it with a flattener for imaging. I use this TS flattener for my Borg and for visual, I get a nice flat field. I note that this flattener states as optimal distance 128mm for under 450mm so probably more for this one as it has an even shorter focal length, so keep in mind the need for plenty of extensions and possible focuser sag unless you sort of balance everything out with something like this.

I am assuming about 45mm or so will be consumed by the sensor to T2 or M48 connection, so the adapter I linked to should more or less work. But basically, you will need something along those lines. If you get a flattener / reducer combo, the optimal distance will be significantly less due to the reducing effect.

Best of luck!

[GlenM]

Thank you for the info, very interesting.. I have been considering trying to convert my 40-150 Olympus for visual as well as imaging. I might be able to buy a adapter to connect to the lens and connect a eyepiece. I have no idea where the focal plane may end up. I think this will take some working out, but it will take my mind off upcoming major surgery?

Thank you again for taking the time with all the info. you are giving me.

 

Glen.

 

 

[nicoscy]

Glen,

I don't think this can be done. Consider that once you connect a lens to a camera, you have something between 40mm - 50mm from connection to the focal plane of the sensor.

If you consider that you need an adapter from the Olympus bayonet, something like this (Not sure if it's this one specifically, but putting it here so that you have an idea) and then you need a T2 focuser (something like this) and then you need a T2 diagonal (recommending the Baader T2 prism diagonal which has the shortest light path), I am not sure you will be able to reach focus. In fact, I am 100% positive you will not be able to do that, as the distance from lens to eyepiece will be too far to reach focus.

You can see my camera mated to the Canon lens above. Consider that there are only 19+11mm = 30mm distance from sensor to camera bayonet and I reach focus. Once you put all the above in place, you are WAY out. Just the diagonal which has the shortest light path available will set you back a bit more than 60mm...

Going back full circle, you asked about the Borg 55FL. Which means you have a very solid budget to even ask about this scope. For the same money, you can get a 71mm flat field refractor (petzval design) with focal ratio of 4.9. Or you can get a triplet and a reducer. Or the Borg and reducer.

So, it comes down to:

1. Your needs seem best served by a short focal length refractor.
2. If you plan to image and want a flat field, you need a flattener. If you also want to reduce the focal length (hence also focal ratio), you need a flattener that is also a reducer. Or you can get a quad flat field refractor.
3. Consider that your lens is multi element to give you a flat field. Refractors do not have so many elements, hence a petzval design or a reducer are necessary, otherwise it's open season for stars that look like comets!
4. Refractor-wise, the Borg is supported by Flo, therefore an excellent choice. You can get the dual visual / imaging package. 

Questions:

1. What objects do you want to image?
2. What do you want to observe with such a short focal length refractor? 

 

[GlenM]

I have now given this careful thought and with your knowledge I am not going to proceed trying to convert the Olympus 40-150 for visual. Thank you for saving me time and money on this little project. I will now look at other options. If I do decide to go with the Borg it would be the f/3.6 imaging/visual version and definitely from FLO.

In answer to question 1 it would be wide field imaging, and 2 would be to just star fields.

 

Thank you very much,

Glen.

 

[nicoscy]

Glen,

My pleasure to help.  As you describe above, the Borg would do. But, if it's for wide field, you can get the job done with say something close to 198mm which the Borg will be - anything that fits a 4/3 system with or without an adapter. A manual lens is probably your best bet since you will not do any auto focusing. Something like this. And an adapter like this. The lens is about $225 - $350 depending on condition and the adapter is dirt cheap. Always use a flat box (or a tablet with a white background and a white piece of cloth on top (to have properly diffused light) to correct for light falloff. You'd do this with the Borg anyway.

I guess I am trying to steer you to get more bang for the buck as they say. If you get the lens and adapter, total cost is GBP 350 max including shipping and taxes. The Borg would set you back all inclusive in excess of GBP 1,200 to set up for both visual and imaging. With the remaining funds, you could grab another scope with a bit more aperture for wide field visual. Something like the new SW72ED, or even this Borg from Flo, which you can use for both imaging and visual.

Some pointers if you do go for the Borg: Get the large non rotating helical focuser, get enough extension tubes as for visual you will need longer OTA Vs imaging at reduced FL, get the Series 60 mounting rings and consider the flattener I recommended above for visual. If you plan to hit nearly 10° TFOV, you need the 2" adapter to be able to use a 2" diagonal and eyepiece.

Ultimately the choice is yours. If you do go for the Borg 55FL, under dark skies and with a flattener and a Pan 24, it is pure ecstasy @ 6.2° TFOV. Barnard's Loop, Andromeda, Witch Head Nebula, North American and Pelican Nebulas, cruising from Sagittarius to Cassiopeia and taking in the vast number of little clusters here and there, yeah, it's good fun. 

I did the Messier Marathon back in 2016 and I had a RACI 50mm finderscope with a Pan 24. Not the Borg. Even with that finderscope, with the perfect conditions we happened to have that evening (truly fantastic transparency), I identified more than 80 Messier objects through the finderscope. I can only imagine what the Borg will do.

Do post your plans! Most interested!

 

[GlenM]

Thanks again for the info. I have looked at alternatives over the past weeks. Paralysis by analysis setting in?

I will of course keep you updated on which way I go. I just need to get through the quadruple by-pass surgery and then I can really plan what I'm going to do. At the moment a decision is difficult.

 

You have given me some excellent things to think about, thank you so much.

 

Glen.

 

[nicoscy]

Glen,

My sincere wishes that surgery goes smoothly and recovery time is as short as possible!

Looking forward to news when you are back on track

[GlenM]

Thank you. I will keep you informed on my decisions. And thank you again for all the advice.

 

Glen.