Barlow lens - suitability
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William Bottaci
Jan 18, 2021, 9:33:14 AM1/18/21
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Hello Chris, I have a pair of 120 mm APM binoculars (just the one
instrument) and another fellow member has a 100 mm Lunt, which would
be equivalent - I'm not aware of anyone else who has large binoculars
with interchangeable eyepieces...
The following is of narrow interest but may also be widely useful.
A Barlow lens is used mostly to increase the magnification, typically
of a 'fast' system, such as f/5 as opposed to f/10 and higher. It can
be a cheaper alternative to another eyepiece or two as you can get
more magnification choices, depending on your spread.
A complication is that you may not be able to use one if your
instrument is so configured that a focus can't be reached. You can
always move outwards with extenders but going inwards you reach a
physical limit. This is known as 'not having enough back focus' (if
going the other way and you need extenders then it's known as a 'back
travel' problem). A Barlow lens needs more of this back focus, and
this is down to both physical and optical design. Even large
Newtonians have this problem because they tend to be fast, say f/4 to
f/6. Think of the shape of the light cone reaching the eyepiece; for
fast systems it's more blunt so less room to play with.
This affects the smaller and especially faster optics, of which
binoculars are so, typically f/5.5. In addition binoculars are not
designed to accept accessories.
The good news. Your binoculars seem good enough that high power
eyepieces can be used. These eyepieces tend to be more awkward to use
but you mostly get used to that.
As an example a magnification of over 100x (both I and the Lunt owner)
is easily practical. The limit is more likely to be how steady the
mount is.
For myself I've used 165x and I can assure anyone that despite the
high power the fact that both eyes are in use makes it a more stable
and comfortable view. Of course it's not 3-d but there is talk of a
3-d effect. I think this is the brain choosing to use the best part of
the view from each eye, whatever that is, but it's real.
So, I know of no way that Barlows can be used, but then they don’t
need to be. I hope this is helpful and comforting.
On tripods, if you are not well equipped I've recently come across this:
https://www.amazon.co.uk/Bosch-BT160-Quick-Clamp-Tripod/dp/B004EIL4R2
which has a flat top and can be used to host a variety of mounts. It
is sturdy and not high-priced, saving on photo-tripods that have
features not required.
Please reply if you need more information; on binocular mounts,
suitable eyepieces etc.
William
On Sat, 16 Jan 2021 at 16:55, Chris Copland <chris....@hotmail.co.uk> wrote:
Hi
I wonder anyone could answer a question for me, I have a 100mm APM
pair of binoculars is it possible to use Barlow lens’ in this
equipment.
Many thank
Chris
instrument) and another fellow member has a 100 mm Lunt, which would
be equivalent - I'm not aware of anyone else who has large binoculars
with interchangeable eyepieces...
The following is of narrow interest but may also be widely useful.
A Barlow lens is used mostly to increase the magnification, typically
of a 'fast' system, such as f/5 as opposed to f/10 and higher. It can
be a cheaper alternative to another eyepiece or two as you can get
more magnification choices, depending on your spread.
A complication is that you may not be able to use one if your
instrument is so configured that a focus can't be reached. You can
always move outwards with extenders but going inwards you reach a
physical limit. This is known as 'not having enough back focus' (if
going the other way and you need extenders then it's known as a 'back
travel' problem). A Barlow lens needs more of this back focus, and
this is down to both physical and optical design. Even large
Newtonians have this problem because they tend to be fast, say f/4 to
f/6. Think of the shape of the light cone reaching the eyepiece; for
fast systems it's more blunt so less room to play with.
This affects the smaller and especially faster optics, of which
binoculars are so, typically f/5.5. In addition binoculars are not
designed to accept accessories.
The good news. Your binoculars seem good enough that high power
eyepieces can be used. These eyepieces tend to be more awkward to use
but you mostly get used to that.
As an example a magnification of over 100x (both I and the Lunt owner)
is easily practical. The limit is more likely to be how steady the
mount is.
For myself I've used 165x and I can assure anyone that despite the
high power the fact that both eyes are in use makes it a more stable
and comfortable view. Of course it's not 3-d but there is talk of a
3-d effect. I think this is the brain choosing to use the best part of
the view from each eye, whatever that is, but it's real.
So, I know of no way that Barlows can be used, but then they don’t
need to be. I hope this is helpful and comforting.
On tripods, if you are not well equipped I've recently come across this:
https://www.amazon.co.uk/Bosch-BT160-Quick-Clamp-Tripod/dp/B004EIL4R2
which has a flat top and can be used to host a variety of mounts. It
is sturdy and not high-priced, saving on photo-tripods that have
features not required.
Please reply if you need more information; on binocular mounts,
suitable eyepieces etc.
William
On Sat, 16 Jan 2021 at 16:55, Chris Copland <chris....@hotmail.co.uk> wrote:
Hi
I wonder anyone could answer a question for me, I have a 100mm APM
pair of binoculars is it possible to use Barlow lens’ in this
equipment.
Many thank
Chris
Chris Copland
Jan 18, 2021, 1:49:16 PM1/18/21
to croydo...@googlegroups.com
Hi William.
Many thanks for your great answer to my question.
The stand you sent through looks more stable than the one I have. Yes please could you send me your recommendation for a 100x lens.,
Many thanks again
Chris
Sent from my iPhone
> On 18 Jan 2021, at 14:33, William Bottaci <w.bo...@gmail.com> wrote:
>
> Hello Chris, I have a pair of 120 mm APM binoculars (just the one
> --
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Many thanks for your great answer to my question.
The stand you sent through looks more stable than the one I have. Yes please could you send me your recommendation for a 100x lens.,
Many thanks again
Chris
Sent from my iPhone
> On 18 Jan 2021, at 14:33, William Bottaci <w.bo...@gmail.com> wrote:
>
> Hello Chris, I have a pair of 120 mm APM binoculars (just the one
> You received this message because you are subscribed to the Google Groups "croydonastro" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to croydonastro...@googlegroups.com.
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paul stenning
Jan 19, 2021, 7:49:27 AM1/19/21
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Hi i am the one with the 100mm lunt binos ,another problem to consider is the loss of detail as the magnification increases ,i have used the teleview 3-6mm zooms ,when it gets to about 3mm which is about x120 magnification the detail really does start to fail to the point that it seems like you can not get it to focus sharply , so I would say it is not very satisfactory at these levels,it really does emphasise the fact that more power is not necessarily a good thing.
if you want to use barlow try using the tele view powermate as these do not suffer from backfocus as does the barlow, i have used these on the binos but i have to agree with William that the loss of stereo vision is a bit too much for me so i stick to using them on my vixen 104mm or on my lovely explore scientific 165mm refractors.
To view this discussion on the web visit https://groups.google.com/d/msgid/croydonastro/VI1PR0902MB1965ABC18E413CACA62ABCD3A4A40%40VI1PR0902MB1965.eurprd09.prod.outlook.com.
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