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04-17-2019, 07:46 PM   #1
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question about Pentax-DA* 300mm F4 ED [IF] SDM

Hi guys,

just got bit confused here about DA* 300mm. What focal distance will this lens give on APSC camera? DA* would suggest it is made for APSC and it would be 300mm on K3 as such, however the description in the lens review on the forum states it is designated for 35mm/full frame. Then the note below on the same tab mentions it works ok for full frame...

SMC Pentax-DA* 300mm F4 ED [IF] SDM Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

Could someone please clarify this?
cheers Ondrej

04-17-2019, 07:58 PM - 1 Like   #2
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The focal length is 300mm. Full stop.

On a crop camera like the K-3, it gives a field of view equivalent to what a 450mm lens would give on a full frame camera like the K-1.

I enjoy my DA*300 on both formats. Although designed as a crop lens, it is 100% full frame compatible.
04-17-2019, 07:59 PM - 5 Likes   #3
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The 300mm on an APS-C will give you ruffly, the same Field of view as a 450mm lens would have on a FF DSLR. The Focal length is always 300mm on either. see here, the focal length is the same, But, simply due to the larger sensor size, the FF captures a wider FoV.


Last edited by cmohr; 04-17-2019 at 11:42 PM. Reason: pic and fix up mistakes
04-17-2019, 08:28 PM - 2 Likes   #4
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QuoteOriginally posted by cmohr Quote
The 300mm on an APS-C will give you ruffly, the same Field of view as a 420mm lens would have on a FF DSLR. The Focal length is always 300mm on either. see here, the focal length is the same, gut simply due to the larger sensor size, the FF captures a wider FoV.
Hi Cmohr

This picture should be added to all "equiverlance " sticky post / threads.

No confusion here


Dave

04-17-2019, 09:13 PM   #5
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Thanks guys, yeah I understand that the focal length is always 300mm and that apsc sensor only crops the field of view.
I also understand that if I take for instance DFA 100mm macro lens and mount it on my K3, the pictures it takes would be same as with using a 150mm apsc designated lens.

What I am trying to figure out is this - do my apsc designated lenses (eg DA35 ltd and DA70 ltd) take photos on K3 that is an equivalent of 35mm/70mm as if I had full frame camera with 35/70mm lens? In other words, if I took K3 with DA70mm ltd and K1 with any 70mm full frame lens and take the same photo, would it be the same?

In other words, when I take DA*300mm (which I undestand to be apsc designated lens) and put it on K3, will I see photos that actually are same as if I took K1 with a full frame 300mm lens or will I see photos that are equivalent to K1 + 450mm full frame lens?

hope it makes more sense

cheers Ondrej
04-17-2019, 09:26 PM   #6
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QuoteOriginally posted by oh_9000 Quote
In other words, when I take DA*300mm (which I undestand to be apsc designated lens) and put it on K3, will I see photos that actually are same as if I took K1 with a full frame 300mm lens or will I see photos that are equivalent to K1 + 450mm full frame lens?
The latter.
The diagram posted by cmohr couldn't be clearer.

Cheers,
Terry
04-17-2019, 09:33 PM   #7
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does that actually mean lenses like DA15mm ltd & DA35mm ltd on K3 show photos that would look same if taken with a full frame camera at 22.5mm and 52.5mm respectively?

Why I am asking this, I have an old 200mm Takumar on K3 and I love the photos' look (focal length). Assuming it is around 300mm equiv on full frame.
If I get DA*300mm on K3 and follow the same logic, it will give me approx 450mm look photos. why there are apsc designated lenses then?

cheers Ondrej
04-17-2019, 09:42 PM - 1 Like   #8
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QuoteOriginally posted by oh_9000 Quote
does that actually mean lenses like DA15mm ltd & DA35mm ltd on K3 show photos that would look same if taken with a full frame camera at 22.5mm and 52.5mm respectively?

Why I am asking this, I have an old 200mm Takumar on K3 and I love the photos' look (focal length). Assuming it is around 300mm equiv on full frame.
If I get DA*300mm on K3 and follow the same logic, it will give me approx 450mm look photos. why there are apsc designated lenses then?

cheers Ondrej
Yes. Basically, your 200mm lens on your K-3 has approx the same field of view as a 300mm lens on a K-1. So yes, The 300mm DA* will be approx the same feild of view as having a 450mm lens on a K-1.

An APS-C lens is designed to produce an image circle that will only cover a Crop APS-C crop sensor, when used on a FF sensor there is bad vignetting or even just a circular image. A FA or DFA lens is designed to project a larger image circle to cover trhe FF sensor.

It comes down to GLass and cost. It's cheaper to build a APS-C lens if all it gets used on is a APS-C camera body.

04-17-2019, 09:45 PM   #9
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QuoteOriginally posted by cmohr Quote
Yes. Basically, your 200mm lens on your K-3 has approx the same field of view as a 300mm lens on a K-1. So yes, The 300mm DA* will be approx the same feild of view as having a 450mm lens on a K-1.

An APS-C lens is designed to produce an image circle that will only cover a Crop APS-C crop sensor, when used on a FF sensor there is bad vignetting or even just a circular image. A FA or DFA lens is designed to project a larger image circle to cover trhe FF sensor.

It comes down to GLass and cost. It's cheaper to build a APS-C lens if all it gets used on is a APS-C camera body.


Makes sense now.
Thank you!

Ondrej
04-17-2019, 09:50 PM   #10
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QuoteOriginally posted by oh_9000 Quote
I also understand that if I take for instance DFA 100mm macro lens and mount it on my K3, the pictures it takes would be same as with using a 150mm apsc designated lens.
Actually, you don't understand. A DFA 100mm, an FA 100mm, and a DA 100mm would all have the same field of view on your K3. The letters in front don't change the focal length.
If you mount all of them on a K1, they would all give a wider field of view than what you see on your K3. But, the DA lens would be dark in the corners because it is designed to project a small image circle. Some DA lenses actually work on a K1 because their image circle is large enough, even though they were originally designed for the small APSC sensor.
Note that there isn't really a DA 100mm. I was just using your example. A better lens would be the 50mm's. The DA 50, DFA 50, FA 50, Tak 50, etc would all have the same view on your K3. Mount them on a K1 and they all give a wider view. The DA 50 would have dark corners on the K1, but its visible area would look exactly the same as the other 50's.

---------- Post added 04-17-19 at 10:32 PM ----------

If you like the Tak 200mm lens on your K3 but you want a more modern lens that will give you the same look, then get the DA* 200mm, or one of the FA* 200mm lenses. They will all give the same field of view as the Tak.

Last edited by Qman; 04-17-2019 at 10:33 PM.
04-17-2019, 10:58 PM   #11
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QuoteOriginally posted by Qman Quote
Actually, you don't understand.

---------- Post added 04-17-19 at 10:32 PM ----------

If you like the Tak 200mm lens on your K3 but you want a more modern lens that will give you the same look, then get the DA* 200mm, or one of the FA* 200mm lenses. They will all give the same field of view as the Tak.


I do understand)
04-17-2019, 11:29 PM   #12
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My dad used to get confused on this topic also. It appears the op now understands, but fit any future reader the summary is:

Any lens with the same focal length gives roughly the same view - even if the lens is designed for a sensor that is larger than the sensor used to create the image.

So a large format (8x10 view camera) 300mm lens on an APSC sensor gives a field of view that isn't appreciably different from an apsc lens. Additionally, the APSC lens would not cover the image circle of the 8x10 camera, but inside the small portion covered, the image would be similar to the image of the larger 300mm 8x10 lens if you masked it's image off to match the amount shown.
04-17-2019, 11:31 PM - 1 Like   #13
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Greetings and welcome. Good questions and a confusing topic. Using Cmohr's excellent picture as the basis, hopefully this composite helps. Even did some math to scale the "printed" images - zoiks!
Attached Images
View Picture EXIF
 Photo 

Last edited by Jim Dandy; 04-17-2019 at 11:48 PM. Reason: correct attribution
04-18-2019, 12:39 AM - 1 Like   #14
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If you have a K3 and do not own a K1, "equivalence" is not actually going to help you. Any 200 mm lens will have the same magnification and FOV on your K3, irrespective of the format it was specifically designed for.
04-18-2019, 04:26 AM - 4 Likes   #15
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Warning.

THIS IS A RANT

Why can’t the cropped sensor and equivalent focal length discussion just go away.

We have been at this for years and years now, and the discussion just does not die.

To be very clear, there are really only 3 properties of a lens that matter, focal length, which defines the magnification ratio of the lens, aperture which determines how big the lens is in diameter, and the image circle that defines how big in diameter the projected image is on the focal plane.

The only difference between any format of lens is the image circle. APSC lenses have an image circle that covers the 16 x 24 mm sensor full frame lenses have an image circle that covers 24 x 36mm sensor medium format lenses have even bigger image circles.

So when you have an APSC lens the only thing that is different than full frame is the absolute dimensions of the image before vignetting takes place
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